Phylogeny of the insulin-like growth factors (IGFS) and receptors: A molecular approach

The IGFs (IGF-I and IGF-II) are essential for normal mammalian growth and development. Their actions are mediated primarily by their interactions with the type I IGF receptor (IGF-I receptor), a transmembrane tyrosine kinase. The ligands and the IGF-I receptor are structurally related to insulin and to the insulin receptor, respectively. Analysis of evolutionary conservation has often provided insights into essential regions of molecules such as hormones and their receptors. The genes for insulin and IGFs have been partially characterized in a number of vertebrate species extending evolutionarily from humans as far back as fish. The sequences of the exons encoding the mature insulin and IGF peptides are highly conserved among vertebrate species, and IGF-I-Iike molecules are found in species whose origins extend back as much as 550 million years. The insulin receptor is also highly conserved in vertebrate species, and an insulinreceptor-like molecule has been characterized in Drosophila. In contrast, IGF-I receptors have only been characterized in mammalian species and partially studied in Xenopus, in which the tyrosine kinase domain is highly conserved. Studies are presently being undertaken to analyze in more detail the regulation of the genes encoding this important family of growth factors and the structure/function relationships in the gene products themselves. © 1993 Wiley-Liss, Inc.     

Experimental Indication in Favor of the Introns-Late Theory: The Receptor Tyrosine Kinase Gene from the Sponge Geodia cydonium

We have analyzed the gene that encodes receptor tyrosine kinase (RTK) from the marine sponge Geodia cydonium, which belongs to the most ancient and simple metazoan groups, the Porifera. RTKs are enzymes found only in metazoa. The sponge gene contains two introns in the extracellular part of the protein. However, the rest of the protein (transmembrane and intracellular part), including the tyrosine kinase (TK)-domain, is encoded by a single exon. In contrast, all TK genes, so far known only from higher animals (vertebrates), contain several introns especially in the TK-domain. The TK-domain of G. cydonium shows similarity with numerous members of receptor as well as nonreceptor TKs. Phylogenetic analysis of the sponge TK-domain indicates that this enzyme branched off first from the common tree of metazoan TK proteins. Consequently, we assume that introns, found in the TK-domains of genes from higher animals, were inserted into these genes after splitting off the sponge taxa from other metazoan organisms (over 600 million years ago). Our results support the view that ancient genes were not ``in pieces.' Received: 8 August 1996 / Accepted: 4 November 1996     

Immortalization and malignant transformation of Eukaryotic cells

The process of cellular transformation has been amply studied in vitro using immortalized cell lines. Immortalized cells never have the normal diploid karyotype, nevertheless, they cannot grow over one another in cell culture (contact inhibition), do not form colonies in soft agar (anchorage-dependent growth) and do not form tumors when injected into immunodeficient rodents. All these characteristics can be obtained with additional chromosome changes. Multiple genetic rearrangements, including whole chromosome and gene copy number gains and losses, chromosome translocations, gene mutations are necessary for establishing the malignant cell phenotype. Most of the experiments detecting transforming ability of genes overexpressed and/or mutated in tumors (oncogenes) were performed using mouse embryonic fibroblasts (MEFs), NIH3T3 mouse fibroblast cell line, human embryonic kidney 293 cell line (HEK293), and human mammary epithelial cell lines (mainly HMECs and MCF10A). These cell lines have abnormal karyotypes and are prone to progress to malignantly transformed cells. This review is aimed at understanding the mechanisms of cell immortalization by different “immortalizing agents”, oncogene-induced cell transformation of immortalized cells and moderate response of the advanced tumors to anticancer therapy in the light of tumor “oncogene and chromosome addiction”, intra-/intertumor heterogeneity, and chromosome instability.     

Chitinase 3-like protein 2 (CHI3L2, YKL-39) activates phosphorylation of extracellular signal-regulated kinases ERK1/ERK2 in human embryonic kidney (HEK293) and human glioblastoma (U87 MG) cells

Human cartilage chitinase 3-like protein 2 (CHI3L2, YKL-39) is secreted by articular chondrocytes, also synoviocytes, lung, and heart. Increased levels of YKL-39 have been demonstrated in synovial fluids of patients with rheumatoid or osteoarthritis as well as in some other pathologies and in malignant tumors, particularly in glioblastomas. It belongs to glycosyl hydrolase family 18 and the most closely related to human cartilage glycoprotein 39 (HC gp-39 or chitinase 3-like protein 1, CHI3L1 or YKL-40), which as it was shown previously, promotes the growth of human synovial cells as well as skin and fetal lung fibroblasts. Dose-dependent growth stimulation was observed when the fibroblastic cell line was exposed to YKL-40 in a concentration range from 0.1 to 2 nM, which is similar to the effective dose of the well characterized mitogen, insulinlike growth factor I. The use of selective inhibitors of the mitogen-activated protein kinase (MAP kinase) signaling pathway indicates that both, YKL-40 and IGF-I are involved in phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/ERK2). Thus YKL-40 initiates a signaling cascade which leads to increased cell proliferation, suggesting that this protein could play some role in the inhibition of apoptosis. We report here that YKL-39, which as YKL-40 has significantly increased expression in glioblastomas, also activates signal-regulated kinases ERK1/ERK2 in human embryonic kidney (HEK293) and human glioblastoma (U87 MG) cells.     

Expression of myelin basic protein and glial fibrillary acidic protein genes in human glial tumors

Analysis of the expression of genes encoding myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP) in human glial tumors was carried out for determination of the expression specificity of these genes according to tumor types and their malignancy. Low levels of MBP mRNA in astrocytoma specimens of malignancy grades II-IV and significantly higher levels in perifocal zones adjacent to them have been determined by Northern hybridization. Diffuse astrocytomas and anaplastic astrocytomas are characterized mostly by a low level of MBP gene expression and high level of GFAP gene expression, but distinct subtypes of diffuse and anaplastic astrocytomas with a high level of GFAP gene expression can also be detected that may be the reflection of different oncogenic pathways. Very low levels or even absence of MBP mRNA were revealed in oligodendroglioma and all oligoastrocytomas. Thus, Northern hybridization data are correlated with serial analysis of gene expression (SAGE). Obtained results show that MBP is a nonspecific marker for tumors of oligodendroglial origin, but determination of relative levels of MBP and GFAP mRNAs may be useful for glial tumor recognition. In such a way, these two genes together with YKL-40 and TSC-22, which we found previously, can be included into the gene panel for determination of so-called “gene signatures” of brain tumors. However, strict requirements in relation to a clinical value of these “gene signatures” cannot be formulated without verifying them on a large number of clinical samples of tumors and valid control.     

Gene structure,transcripts and calciotropic effects of the PTH family of peptides in <Emphasis Type="Italic">Xenopus</Emphasis> and chicken

Background  

Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) belong to a family of endocrine factors that share a highly conserved N-terminal region (amino acids 1-34) and play key roles in calcium homeostasis, bone formation and skeletal development. Recently, PTH-like peptide (PTH-L) was identified in teleost fish raising questions about the evolution of these proteins. Although PTH and PTHrP have been intensively studied in mammals their function in other vertebrates is poorly documented. Amphibians and birds occupy unique phylogenetic positions, the former at the transition of aquatic to terrestrial life and the latter at the transition to homeothermy. Moreover, both organisms have characteristics indicative of a complex system in calcium regulation. This study investigated PTH family evolution in vertebrates with special emphasis on Xenopus and chicken.