Modulation of adrenal cell functions by cadmium salts: 2. Sites affected by CdCl2 during unstimulated steroid synthesis

In previous studies cadmium chloride (CdCl₂) nonlethally inhibited Y-1 adrenal mouse adrenal tumour cell 20-dihydroxyprogesterone (20DHP) secretion, affecting unstimulated and stimulated steroidogenic pathway sites differently. We studied CdCl₂ effects on unstimulated steroidogenesis using Y-1 cells incubated 0.5 h in medium with or without cadmium (using the concentration that inhibited ACTH-stimulated steroid secretion by 50%). Exogenously added 20-hydroxycholesterol (20OHC), 22(R)-hydroxycholesterol (22OHC), 25-hydroxycholesterol (25OHC), pregnenolone (PREG), or progesterone (PROG) were used to bypass any rate-limited steroidogenic pathway sites that CdCl₂ might inhibit. 25OHC is a biologically active nonpathway steroid, while 20OHC, 22OHC, PREG, and PROG are pathway steroids; each increased unstimulated 20DHP secretion nearly 10-fold. Although CdCl₂ could not reduce dibutyryl cyclic AMP- (dbcAMP)-stimulated 20DHP secretion significantly, it did significantly reduce basal and 25OHC-induced 20DHP secretion 25% below untreated levels. When 20OHC, 22OHC, PREG, or PROG were incubated with unstimulated Y-1 cells, their synthesis into 20DHP was unaffected by cadmium. dbcAMP bypasses the plasma membrane enzyme complex that synthesizes intracellular cAMP during exogenous ACTH stimulation; dbcAMP was not inhibited by CdCl₂. The rate-limited step accelerated by cAMP involves plasma membrane and/or cytoplasmic cholesterol transport to and through outer and inner mitochondrial membranes before the cholesterol is synthesized into pregnenolone by side-chain cleavage enzymes on the inner membrane matrix face. Little is known regarding the mechanisms controlling unstimulated steroidogenesis. Under unstimulated conditions the 25-, 20- and 22(R)-monohydroxyls of cholesterol facilitate plasma membrane, cytoplasm and inner and outer mitochondrial solubility, diffusion and/or transport to bypass rate-limited steps and augment unstimulated steroid synthesis. Since conversion of endogenous mitochondrial cholesterol and 25OHC, but not dbcAMP-mobilized cytoplasmic cholesterol, 20OHC or 22OHC conversion, to 20DHP is inhibited by CdCl₂, this suggests that (a) control of mitochondrial cholesterol supplies is independent of the cAMP-regulated mitochondrial steps in the 20DHP steroid synthetic pathway, (b) CdCl₂ specifically inhibited endogenous mitochondrial cholesterol and 25OHC utilization, (c) CdCl₂ toxicity may affect adrenal, testicular, ovarian, and placental basal steroidogenic functions, and (d) 25OHC may be a useful compound to examine unstimulated steroid synthesisAbbreviations ACTH adrenocorticotropin - ANOVA analysis of variance - CdCl₂ cadmium chloride - cAMP cyclic 3,5-adenosine monophosphate - DMSO dimethylsulfoxide - DNA deoxyribonucleic acid - FMEM serum-free Eagle's Minimum Essential Medium - Hepes N-2-hydroxyethyl-piperazine-N-1,2-ethanesulfonic acid - 20OHC 20-hydroxycholesterol - 22OHC 22(R)-hydroxycholesterol - 25OHC 25-hydroxycholesterol - IC_50' concentration inhibiting stimulated steroid secretion by 50% - IU international unit - MEM Eagle's Minimum Essential Medium - P450scc cytochrome P450 side-chain cleavage enzyme - PREG pregnenolone - PROG progesterone - RNA ribonucleic acid - SEM standard error of the mean - SMEM serum-containing Eagle's Minimum Essential Medium - 20DHP 20-hydroxy-4-pregnen-3-one     

A ROCK inhibitor promotes keratinocyte survival and paracrine secretion,enhancing establishment of primary human melanocytes and melanocyte–keratinocyte co‐cultures

Primary melanocytes isolated from skin and expanded in culture have been widely used for laboratory research and clinical applications. The conventional method to isolate primary melanocytes from skin usually requires about 3–4 weeks of culture for melanocytes to grow sufficiently to passage. Considering that melanocytes comprise only 3%–7% of epidermal cells in normal human skin, it would be extremely helpful to increase the isolation efficiency and shorten the initial culture time to quickly meet various application needs. Here, we report that adding Y‐27632, a Rho kinase inhibitor, into the initial culture medium for 2 days can dramatically increase the yield of melanocytes. We found that Y‐27632 can promote keratinocyte attachment and survival in the melanocyte culture system, resulting in not only better recovery, but also increased proliferation of melanocytes by a paracrine signaling pathway. More specifically, Y‐27632 significantly induced keratinocyte expression of stem cell factor, which played an important role in enhancing the growth of melanocytes. In summary, Y‐27632 could profoundly enhance the yield of primary melanocytes in the initial culture through paracrine effects on keratinocytes.     

ROCK and mDia1 antagonize in Rho-dependent Rac activation in Swiss 3T3 fibroblasts

The small GTPase Rho acts on two effectors, ROCK and mDia1, and induces stress fibers and focal adhesions. However, how ROCK and mDia1 individually regulate signals and dynamics of these structures remains unknown. We stimulated serum-starved Swiss 3T3 fibroblasts with LPA and compared the effects of C3 exoenzyme, a Rho inhibitor, with those of Y-27632, a ROCK inhibitor. Y-27632 treatment suppressed LPA-induced formation of stress fibers and focal adhesions as did C3 exoenzyme but induced membrane ruffles and focal complexes, which were absent in the C3 exoenzyme-treated cells. This phenotype was suppressed by expression of N17Rac. Consistently, the amount of GTP-Rac increased significantly by Y-27632 in LPA-stimulated cells. Biochemically, Y-27632 suppressed tyrosine phosphorylation of paxillin and focal adhesion kinase and not that of Cas. Inhibition of Cas phosphorylation with PP1 or expression of a dominant negative Cas mutant inhibited Y-27632-induced membrane ruffle formation. Moreover, Crk-II mutants lacking in binding to either phosphorylated Cas or DOCK180 suppressed the Y-27632-induced membrane ruffle formation. Finally, expression of a dominant negative mDia1 mutant also inhibited the membrane ruffle formation by Y-27632. Thus, these results have revealed the Rho-dependent Rac activation signaling that is mediated by mDia1 through Cas phosphorylation and antagonized by the action of ROCK.     

Rho‐kinase inhibitor Y‐27632 increases cellular proliferation and migration in human foreskin fibroblast cells

The idea of direct differentiation of somatic cells into other differentiated cell types has attracted a great interest recently. Rho‐kinase inhibitor Y‐27632 (ROCKi) is a potential drug molecule, which has been reported to support the gene expressions typical for the chondrocytes, thus restricting their phenotypic conversion to fibroblastic cells upon the cellular expansion. In this study, we have investigated the short‐term biological responses of ROCKi to human primary foreskin fibroblasts. The fibroblast cells were exposed to 1 and 10 μM ROCKi treatments. A proteomics analysis revealed expression changes of 56 proteins, and a further protein pathway analysis suggested their association with the cell morphology, the organization, and the increased cellular movement and the proliferation. These functional responses were confirmed by a Cell‐IQ time‐lapse imaging analysis. Rho‐kinase inhibitor treatment increased the cellular proliferation up to twofold during the first 12 h, and a wound model based migration assay showed 50% faster filling of the mechanically generated wound area. Additionally, significantly less vinculin‐associated focal adhesions were present in the ROCKi‐treated cells. Despite the marked changes in the cell behavior, ROCKi was not able to induce the expression of the chondrocyte‐specific genes, such as procollagen α₁(II) and aggrecan.     

A role of activated Sonic hedgehog signaling for the cellular proliferation of oral squamous cell carcinoma cell line

Sonic hedgehog (Shh) is a secreted morphogen crucial for appropriate cellular proliferation during mammalian development. The activated Shh signaling is known to predispose to human tumors such as medulloblastoma and basal cell carcinoma, while a role of Shh signaling in the other common tumors is still controversial. Here we showed the overexpression of Shh in five cell lines among 14 human oral squamous cell carcinoma (OSCC) cell lines. One of the Shh-expressing OSCC cell lines HSQ-89 showed the inhibition of G1/S transition and apoptotic cell death by treatment with Cyclopamine, a steroidal alkaloid that blocks the intracellular Shh signaling. Furthermore, we found that treatment with Y-27632, a specific inhibitor of Rho-associated kinase, mimicked the effect of Cyclopamine on the cell cycle progression of HSQ-89. Our study revealed the involvement of activated Shh signaling in the cellular proliferation of OSCC cells, indicating Shh signaling might be a good therapeutic target for OSCC.     

A role for Rho kinase in vascular contraction evoked by sodium fluoride

Agonist and depolarization-induced vascular smooth muscle contractions involve the activation of Rho-kinase pathway. However, there are no reports addressing the question whether this pathway is involved in NaF-induced vascular contractions. We hypothesized that Rho-kinase plays a role in vascular contraction evoked by sodium fluoride in rat aortae. In both physiological salt solution and calcium-free solution with 2 mM EGTA, cumulative addition of NaF increased vascular tension in concentration-dependent manners. Effects of Rho-kinase inhibitor (Y27632) on phosphorylation of myosin light chain (MLC20) and myosin targeting subunit (MYPT1(Thr696)) of myosin light chain phosphatase as well as NaF-induced contractions were determined using isolated tissue and the Western blot experiments. Y27632 inhibited NaF-induced contractions in a concentration-dependent manner. NaF increased phosphorylation of MLC20 and MYPT1(Thr696), which were also inhibited by Y27632. However, MLCK inhibitor (ML-7) or PKC inhibitor (Ro31-8220) did not inhibit the NaF-induced contraction. These results indicate that activation of Rho-kinase and the subsequent phosphorylation of MYPT1(Thr696) play important roles in NaF-induced contraction of rat aortae.     

Aldosterone induces myofibroblastic transdifferentiation and collagen gene expression through the Rho-kinase dependent signaling pathway in rat mesangial cells

There is accumulating evidence indicating the role of aldosterone in the pathogenesis of hypertension and renal injury. In this study, we investigated the role of the Rho-kinase dependent signaling pathway in aldosterone-induced myofibroblastic transdifferentiation and collagen gene expression in rat mesangial cells (RMCs). Stimulation with aldosterone (1 nmol/L) significantly increased phosphorylation of myosin phosphatase target subunit-1 (MYPT-1), a marker of Rho-kinase activity, with a peak at 20 min in RMCs. Pre-incubation with a selective mineralocorticoid receptor antagonist, eplerenone (10 µmol/L), or a specific Rho-kinase inhibitor, Y27632 (10 µmol/L), attenuated the aldosterone-induced increase in MYPT-1 phosphorylation. Aldosterone also induced hypertrophy in RMCs, accompanied by an increase in actin polymerization and expression of α-smooth muscle actin (α-SMA), a myofibroblastic transdifferentiation marker. Collagen type I, III and IV mRNA levels were also increased with aldosterone stimulation. Pre-treatment with eplerenone or Y27632 prevented the aldosterone-induced cell hypertrophy, actin polymerization, the increase in α-SMA expression and the increases of collagen type I, III, IV mRNA levels in RMCs. These results suggest that aldosterone-induced mesangial cell hypertrophy is associated with cell transformation, leading to an increase in collagen gene expression via the Rho-kinase dependent signaling pathway.     

Intergeneric protoplast fusion between Kluyveromyces and Saccharomyces cerevisiae – to produce sorbitol from Jerusalem artichokes

The construction of inulin-assimilating and sorbitol-producing fusants was achieved by intergeneric protoplast fusion between Kluyveromyces sp. Y-85 and Saccharomyces cerevisiae E-15. The cells of parental strains were pretreated with 0.1% EDTA (w/v) and 2-mercaptoethanol (0.1%, v/v) and then exposed to 2.0% (w/v) Zymolase at 30 °C for 30–40 min. The optimized fusion condition demonstrated that with the presence of 30% (w/v) polyethylene glycol 6000 (PEG-6000) and 10 mM CaCl₂ for 30 min, the fusion frequency reached 2.64 fusants/10⁶ parental cells. The fusants were screened by different characters between two parental strains and further identified by DNA contents, inulinase activity and sorbitol productivity. One of the genetically stable fusants, Strain F27, reached a maximal sorbitol production of 4.87 g/100 ml under optimal fermentation condition.     

Degenerative muscle fiber accelerates adipogenesis of intramuscular cells via RhoA signaling pathway

In some pathological conditions such as Duchenne muscular dystrophy, it has been known that a fatty infiltration in skeletal muscle is often observed and that is also one of primary factors to induce marked decline of muscular strength. However, the mechanism of fatty infiltration, cellular origin of accumulated adipocytes and its significance are not fully understood. The fact that persistent degenerative muscle fibers are present on dystrophic muscle leads us to hypothesize that muscle fiber condition affects fatty infiltration in skeletal muscle. We employed a single fiber culture system to determine whether fiber condition affects an appearance of adipocytes on the fibers. Artificially hyper-contracted muscle fibers (HCF), generated from isolated intact fibers (IF) of rat extensor digitrum longus muscle, were maintained as non-adherent cultures for 5–7 days. Interestingly, there appeared to be considerable numbers of mature adipocytes on HCF, whereas no adipocytes were seen on IF, indicating that cells on HCF spontaneously differentiated into mature adipocytes. Activation of RhoA signaling by the addition of thrombin decreased the number of adipocytes on HCF in a dose-dependent manner, whereas the number of MyoD-positive myoblasts increased. In contrast, Y-27632, a specific inhibitor of Rho kinases (ROCK), induced adipogenic differentiation of cells derived from IF. In addition, administration of Y-27632 into mouse regenerating muscle resulted in fat accumulation in the muscle. Taken together, the present studies clearly demonstrated that muscle fiber condition affects fat accumulation in skeletal muscle and that is possibly mediated by the RhoA signaling pathway.     

Use of a sequential strategy of experimental design to optimize the inulinase production in a batch bioreactor

A potential application of inulinase in the food industry is the production of fructoligosaccharides (FOS) by the transfructosilation of sucrose. The FOSs present many interesting functional properties besides their ability to increase the shelf-life and flavor of many products. The use of an industrial medium represents a good alternative to producing inulinase at low cost, since the activity may improve, or at least remain the same, as that obtained using a synthetic medium. This work was an optimization study of the inulinase production by Kluyveromyces marxianus NRRL Y-7571 using industrial pre-treated culture medium in a bioreactor employing a sequential strategy of experimental design. Initially, a Plackett–Burman (Screening Design) design was used, where the studied variables were molasses, corn steep liquor, yeast extract concentration, and agitation and aeration rates. After the analysis of the effects, a central composite rotational design (CCRD) was carried out. The optimized condition for the inulinase production was: 250 g/l of molasses, 80 g/l of corn steep liquor, 6 g/l of yeast extract, 300 rpm of agitation and 1.5 vvm aeration rate, which resulted in an enzymatic activity of 1,317 ± 65 U/ml.