Transformation by T-antigen and other oncogenes delays Hsp25 accumulation in heat shocked NIH 3T3 fibroblasts

We have recently reported that transformation of murine NIH 3T3 cells by v-fos oncogene interfered with Hsp70 and Hsp25 accumulation after heat shock. Here, we have investigated the effect mediated by other oncogenes on the accumulation of these stress proteins. We report that T-antigen transformation of NIH 3T3 cells delayed and reduced the accumulation of Hsp25 after heat shock and decreased the heat-mediated phosphorylation of this protein. This decreased level of Hsp25 correlated with a reduced accumulation of the corresponding mRNA and was related to T-antigen level. In contrast, T-antigen had no effect on the expression of the major stress protein Hsp70 nor did it interfere with the level of Hsp90 or Hsp60. We report also that v-src or Ha-ras oncogenes delayed Hsp25 accumulation after heat shock but that only v-src reduced the heat-induced phosphorylation of this protein. v-src, but not Ha-ras, interfered with Hsp70 expression and none of these oncogenes had an effect on Hsp60 or Hsp90 levels. Taken together, these observations suggest that an altered accumulation of Hsp25 after heat shock is a common characteristic of NIH 3T3 fibroblasts transformed by different oncogenes.     

Bradykinin-induced oscillations of cell membrane potential in cells expressing the Ha-ras oncogene

Products of ras genes are putative elements of growth factor signal transduction. However, the mechanism of action of these proteins in normal and malignant growth is as yet obscure. To test for functional consequences of ras oncogene expression, electrophysiological experiments were performed on NIH-3T3 fibroblasts transfected with a transforming Ha-ras MMTV-LTR construct expressing the oncogene on treatment with dexamethasone (+ras). Transfected cells in the absence of dexamethasone (-ras) and nontransfected cells in the presence of dexamethasone (oras) served as controls. In -ras and oras, bradykinin induces a single, transient hyperpolarization. In +ras, bradykinin elicits oscillations of cell membrane potential throughout the presence of the hormone by activation of calcium-sensitive K+ channels. The oscillations of cell membrane potential are abolished in the absence of extracellular calcium. As evident from fura 2 fluorescence, bradykinin leads to a transient increase of intracellular calcium both in the presence and absence of extracellular calcium. Oscillations of intracellular calcium could be observed in +ras cells, if bradykinin was applied at reduced extracellular sodium concentration possibly to impair calcium extrusion via the sodium/calcium exchange. Bradykinin induces oscillations of cell membrane potential similarly in -ras cells loaded with GTP[S], a nonhydrolyzable analogue of GTP. Thus, the altered response of ras oncogene expressing cells to bradykinin relates to the GTP binding property of the ras protein. It is concluded that in cells expressing ras oncogene but not in other fibroblasts bradykinin mimicks the effect of growth factors on the cell membrane.     

Expression of the murine small heat shock proteins hsp 25 and alpha B crystallin in the absence of stress

Stress induces the synthesis of several large and small heat shock proteins (hsp's). Two related small hsp's, hsp25 and alpha B crystallin exist in mice. alpha B crystallin is an abundant protein in several tissues even in the absence of stress. Particularly high amounts accumulate in the eye lens. Here we show that hsp25 is likewise constitutively expressed in many normal adult tissues. In the absence of stress the protein is most abundant in the eye lens, heart, stomach, colon, lung, and bladder. The stress-independent expression pattern of the two small hsp's is distinct. In several tissues the amount of hsp25 exceeds that accumulating in NIH 3T3 fibroblasts in response to heat stress. hsp25, like alpha B crystallin, exists in a highly aggregated form in the eye lens. The expression of hsp25 and alpha B crystallin in normal tissues suggests an essential, but distinct function of the two related proteins under standard physiological conditions.     

Ras (proto)oncogene induces N-linked carbohydrate modification: temporal relationship with induction of invasive potential

The effect of expression of the ras oncogene on protein glycosylation was studied. VSV G-protein and class I histocompatibility antigens were analysed to monitor ras-mediated changes in glycosylation. Transient expression of the c-Ha-ras oncogene, introduced into NIH 3T3 cells by the DEAE-dextran method, altered protein glycosylation within 25 h of transfection. The same result was obtained after dexamethasone-induced expression of p21-ras in stable NIH 3T3 transfectants containing either an activated Ha-ras oncogene or a normal N-ras proto-oncogene under control of the glucocorticoid-inducible MMTV promoter. The alteration of cell surface carbohydrates, induced by the ras (proto)oncogene and the subsequent acquisition of invasive potential, occurred prior to morphological transformation.     

Effect of a dominant inhibitory Ha-ras mutation on mitogenic signal transduction in NIH 3T3 cells.

We used a dominant inhibitory mutation of c-Ha-ras which changes Ser-17 to Asn-17 in the gene product p21 [p21(Asn-17)Ha-ras] to investigate ras function in mitogenic signal transduction. An NIH 3T3 cell line [NIH(M17)] was isolated that displayed inducible expression of the mutant Ha-ras gene (Ha-ras Asn-17) via the mouse mammary tumor virus long terminal repeat and was growth inhibited by dexamethasone. The effect of dexamethasone induction on response of quiescent NIH(M17) cells to mitogens was then analyzed. Stimulation of DNA synthesis by epidermal growth factor (EGF) and 12-O-tetradecanoylphorbol-13-acetate (TPA) was completely blocked by p21(Asn-17) expression, and stimulation by serum, fibroblast growth factor, and platelet-derived growth factor was partially inhibited. However, the induction of fos, jun, and myc by EGF and TPA was not significantly inhibited in this cell line. An effect of p21(Asn-17) on fos induction was, however, demonstrated in transient expression assays in which quiescent NIH 3T3 cells were cotransfected with a fos-cat receptor plasmid plus a Ha-ras Asn-17 expression vector. In this assay, p21(Asn-17) inhibited chloramphenicol acetyltransferase expression induced by EGF and other growth factors. In contrast to its effect on DNA synthesis, however, Ha-ras Asn-17 expression did not inhibit fos-cat expression induced by TPA. Conversely, downregulation of protein kinase C did not inhibit fos-cat induction by activated ras or other oncogenes. These results suggest that ras proteins are involved in at least two parallel mitogenic signal transduction pathways, one of which is independent of protein kinase C. Although either pathway alone appears to be sufficient to induce fos, both appear to be necessary to induce the full mitogenic response.     

Presentation of alpha B-crystallin to T cells in active multiple sclerosis lesions: an early event following inflammatory demyelination

In the development of multiple sclerosis (MS), (re)activation of infiltrating T cells by myelin-derived Ags is considered to be a crucial step. Previously, alpha B-crystallin has been shown to be an important myelin Ag to human T cells. Since alpha B-crystallin is an intracellular heat shock protein, the question arises at what stage, if any, during lesional development in MS this Ag becomes available for CD4+ T cells. In 3 of 10 active MS lesions, alpha B-crystallin could be detected inside phagocytic vesicles of perivascular macrophages, colocalizing with myelin basic protein and myelin oligodendrocyte glycoprotein (MOG). Although the detectability of MOG in phagosomes is considered as a marker for very recent demyelination, MOG was detected in more macrophages and in more lesions than alpha B-crystallin. The disappearance of alpha B-crystallin from macrophages even before MOG was confirmed by in vitro studies; within 6 h after myelin-uptake alpha B-crystallin disappears from the phagosomes. Alpha B-crystallin-containing macrophages colocalized with infiltrating T cells and they were characterized by expression of MHC class II, CD40, and CD80. To examine functional presentation of myelin Ags to T cells, purified macrophages were pulsed in vitro with whole myelin membranes. These macrophages activated both myelin-primed and alpha B-crystallin-primed T cells in terms of proliferation and IFN-gamma secretion. In addition, alpha B-crystallin-pulsed macrophages activated myelin-primed T cells to the same extent as myelin-pulsed macrophages, whereas myelin basic protein-pulsed macrophages triggered no response at all. These data indicate that, in active MS lesions, alpha B-crystallin is available for functional presentation to T cells early during inflammatory demyelination.     

The small heat shock protein alpha B-crystallin is a novel inhibitor of TRAIL-induced apoptosis that suppresses the activation of caspase-3

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor alpha family of cytokines that preferentially induces apoptosis in transformed cells, making it a promising cancer therapy. However, many neoplasms are resistant to TRAIL-induced apoptosis by mechanisms that are poorly understood. We demonstrate that the expression of the small heat shock protein alpha B-crystallin (but not other heat shock proteins or apoptosis-regulating proteins) correlates with TRAIL resistance in a panel of human cancer cell lines. Stable expression of wild-type alpha B-crystallin, but not a pseudophosphorylation mutant impaired in its assembly and chaperone function, protects cancer cells from TRAIL-induced caspase-3 activation and apoptosis in vitro. Furthermore, selective inhibition of alpha B-crystallin expression by RNA interference sensitizes cancer cells to TRAIL. In addition, wild-type alpha B-crystallin promotes xenograft tumor growth and inhibits TRAIL-induced apoptosis in vivo in nude mice, whereas a pseudophosphorylation alpha B-crystallin mutant impaired in its anti-apoptotic function inhibits xenograft tumor growth. Collectively, these findings indicate that alpha B-crystallin is a novel regulator of TRAIL-induced apoptosis and tumor growth. Moreover, these results demonstrate that targeted inhibition of alpha B-crystallin promotes TRAIL-induced apoptosis, thereby suggesting a novel strategy to overcome TRAIL resistance in cancer.     

αB-Crystallin Interacts with Cytoplasmic Intermediate Filament Bundles during Mitosis

The small heat-shock protein αB-crystallin interacts with intermediate filament proteins. Using cosedimentation assay, we showed previously that in vitro binding of αB-crystallin to peripherin and vimentin was temperature-dependent. Furthermore, when NIH 3T3 cells were submitted to different stress conditions a dynamic reorganization of the intermediate filament network was observed concomitantly with the recruitment of αB-crystallins on the intermediate filament proteins. Thus, the intracellular state of αB-crystallin correlated directly with the remodeling of the intermediate filament network in response to stress. Here, we show data suggesting that αB-crystallin is implicated in remodeling of intermediate filaments during cell division. We investigated the intracellular distribution of αB-crystallin in naturally occurring mitotic NIH 3T3 cells and in neuroblastoma N2a and N1E115 cells. In NIH 3T3 cells, αB-crystallin remained diffused throughout the cell cycle. Subcellular fractionation of αB-crystallin showed that αB-crystallin remained in the cytosolic compartment during mitosis. Furthermore, αB-crystallin accumulated in mitotically arrested NIH 3T3 cells. This increased level of αB-crystallin protein was due to an increased level of αB-crystallin mRNA in mitotic NIH 3T3 cells. In the neuroblastoma cells, the intermediate filaments were rearranged into thick cable-like structures and αB-crystallin was recruited onto them. In neuroblastoma N2a cells the level of expression did not change during the cell cycle. However, a small fraction of αB-crystallin switched onto the insoluble fraction in mitotically arrested N2a cells. Our results suggested that depending on the state of rearrangement of the intermediate filament network during mitosis αB-crystallin was either recruited onto the intermediate filaments or upregulated in the cytosolic compartment.     

Sense and antisense modification of glial alpha B-crystallin production results in alterations of stress fiber formation and thermoresistance

The phenotypic effects of selectively altering the levels of alpha B- crystallin in cultured glial cells were analyzed using sense and antisense approaches. Rat C6 glioma cells and human U-373MG glioma cells were transfected with a rat alpha B-crystallin sense cDNA or an antisense cDNA regulated by a Rous sarcoma virus promoter to alter cellular levels of alpha B-crystallin. The antisense strategy resulted in decreased alpha B-crystallin levels, as revealed by Western blot and immunocytochemical analyses. The reduced alpha B-crystallin expression was accompanied by alterations in cellular phenotype: (a) a reduction of cell size and/or a slender cell morphology; (b) a disorganized microfilament network; and (c) a reduction of cell adhesiveness. Like HSP27, the presence of additional alpha B-crystallin protein confers a thermoresistant phenotype to stable transfectants. Thus, alpha B- crystallin in glioma cells plays a role in their thermal resistance and may contribute to the stability of cytoskeletal organization.     

The effects of ras gene expression on glucocorticoid receptors in mouse fibroblasts

Analysis of induction of glutamine synthetase activity by dexamethasone showed a 2-fold increase in NIH3T3 but no change in NIH3T3 ras (EJ-ras) cells. The observed increase could be abolished by the antagonist RU486. The lack of response in ras transformed cells might reflect oncoprotein effects on the glucocorticoid receptor (GR). Several GR parameters were studied in order to clarify this point. Total GR level was the same for both cells; cytoplasmic receptor level however, was 3 times lower in NIH3T3 ras than in NIH3T3 cells. Hormone-receptor binding affinity, specificity, thermostability, sedimentation coefficient, molecular weight as well as the cytoplasmic GR transformation ratio were similar for the two cell lines. On the other hand, the fraction of the total receptor pool involved with the recycling process was approximately 20% lower in NIH3T3 ras than in NIH3T3 cells. After 24 h of dexamethasone treatment, no GR down regulation was observed in NIH3T3 ras cells, whereas normal NIH3T3 cells exhibited a decrease of GR binding capacity around 80%. Further studies are necessary to define the mechanisms underlying the association between glucocorticoid insensitivity, and modifications in the GR nuclear/cytoplasmic ratio, in the recycling GR fraction and in the down-regulation process observed in ras transformed cells.     

Activating mutations for transformation by p53 produce a gene product that forms an hsc70-p53 complex with an altered half-life.

The 11-4 p53 cDNA clone failed to transform primary rat fibroblasts when cotransfected with the ras oncogene. Two linker insertion mutations at amino acid 158 or 215 (of 390 amino acids) activated this p53 cDNA for transformation with ras. These mutant cDNAs produced a p53 protein that lacked an epitope, recognized by monoclonal antibody PAb246 (localized at amino acids 88 to 110 in the protein) and preferentially bound to a heat shock protein, hsc70. In rat cells transformed by a genomic p53 clone plus ras, two populations of p53 proteins were detected, PAb246+ and PAb246-, which did or did not bind to this monoclonal antibody, respectively. The PAb246- p53 preferentially associated with hsc70, and this protein had a half-life 4- to 20-fold longer than free p53 (PAb246+). These data suggest a possible functional role for hsc70 in the transformation process. cDNAs for p53 derived from methylcholanthrene-transformed cells transform rat cells in cooperation with the ras oncogene and produce a protein that bound with the heat shock proteins. Recombinant clones produced between a Meth A cDNA and 11-4 were tested for the ability to transform rat cells. A single amino acid substitution at residue 132 was sufficient to activate the 11-4 p53 cDNA for transformation. These studies have identified a region between amino acids 132 and 215 in the p53 protein which, when mutated, can activate the p53 cDNA. These results also call into question what the correct p53 wild-type sequence is and whether a wild-type p53 gene can transform cells in culture.     

Glucocorticoid dexamethasone reversibly complements EJ-RAS oncogene to transform mouse embryo BALB-3T3 cells

EJ-A is a Balb-3T3 transfectant cell line that bears a small number of EJ-ras oncogene copies/cell, has low EJ-ras expression, and resembles the parental cell line in displaying a non-transformed phenotype. The glucocorticoid hormone dexamethasone reversibly induces transformation traits in EJ-A cells, namely: 1) morphological transformation; 2) increased growth rate and saturation density; 3) reduced G1 length; and 4) independence of the FGF requirement to initiate DNA synthesis. Western blot analysis revealed that dexamethasone does not increase the p21ras protein intracellular level. beta-IFN, added to the culture medium, does not suppress the dexamethasone-induced growth stimulation and morphological transformation. Therefore, glucocorticoid hormones can complement low EJ-ras expression to transform Balb-3T3 cells, by a mechanism that is likely to be independent of p21ras increase and beta-IFN decrease.     

Coordinate regulation of the levels of type III and type I collagen mRNA in most but not all mouse fibroblasts

A mouse genomic clone was isolated by cross-hybridization with a DNA fragment which codes for the NH2-propeptide of chick alpha1(III) collagen. The region of cross-hybridization within the mouse clone was localized, its sequence determined, and an exon coding for the NH2-propeptide of mouse alpha1(III) collagen was identified. This DNA fragment hybridizes to an RNA species of approximately 5300 nucleotides, slightly larger than the major alpha2(I) collagen RNA species. The mouse type III collagen probe was used to examine the effect of transformation on alpha1(III) collagen RNA levels in mouse fibroblasts. The levels of type III and type I collagen mRNA levels were compared in control and sarcoma virus-transformed murine cell lines, as well as in NIH 3T3 cells transformed by members of the human ras oncogenes. The levels of type III RNA decreased about 10-15-fold in Moloney sarcoma virus-transformed cells and in a cell line transformed with a v-mos-containing plasmid, but showed only a 50% decrease in a Kirsten murine sarcoma virus-transformed BALB 3T3 cell line, and increased 4-fold in a Rous sarcoma virus (RSV)-transformed BALB 3T3 cell line. In contrast, the levels of alpha2(I) collagen mRNA are 8- to 10-fold lower in all these cell lines when compared to untransformed cells. NIH 3T3 cells transformed with two human ras oncogenes showed decreased levels of alpha2(I) and alpha1(III) mRNAs. In contrast to the RSV-transformed mouse cell line, RSV-transformed chick embryo fibroblasts contained much smaller amounts of type III RNA than control chick embryo fibroblasts. We conclude that the levels of alpha1(III) and alpha2(I) collagen mRNA are often but not necessarily coordinately regulated by transformation in mouse cells.     

Preparation and characteristics of a new transformed cell line G11 by transfection of NIH/3T3 mouse fibroblasts with DNA from the SA7 oncogene of simian adenovirus

Murine fibroblasts NIH 3T3 were transfected with the plasmid pASP containing simian adenovirus oncogene insertion. Focus forming transformants were cloned with a final dilution technique and a new cell line G11 was created as a result. Transformed status of this cell line is evidenced by changes in morphology, specific cytochemical and adhesion properties, ability to grow in semisolid agar and FCS concentration growth independence. Presence of intact integrated E1a-region of adenovirus SA7 oncogene was shown by blot-hybridization technique. Transformed status of G11 cells can be explained by integration of SA7 oncogene, that is evidenced indirectly by the increased resistance to heat shock.