A novel member of the serine/threonine protein kinase gene family, designated sgk, for serum and glucocorticoid-regulated kinase, was identified in a differential screen for glucocorticoid-inducible transcripts expressed in the Con8.hd6 rat mammary tumor cell line. sgk encodes a protein of 49 kDa which has significant sequence homology (45 to 55% identity) throughout its catalytic domain with rac protein kinase, the protein kinase C family, ribosomal protein S6 kinase, and cyclic AMP-dependent protein kinase. sgk mRNA is expressed in most adult rat tissues, with the highest levels in the thymus, ovary, and lung, as well as in several rodent and human cell lines. sgk mRNA was stimulated by glucocorticoids and by serum within 30 min, and both inductions were independent of de novo protein synthesis. The transcriptional regulation by glucocorticoids is a primary response, since the promoter of sgk contains a glucocorticoid response element consensus sequence 1.0 kb upstream of the start of transcription which is able to stimulate chloramphenicol acetyltransferase reporter gene activity in a dexamethasone-dependent manner. Antibodies that specifically recognize sgk-encoded protein on an immunoblot were generated. This protein was shown to increase in abundance with glucocorticoid treatment in a manner which paralleled the mRNA accumulation. This is the first report of a presumed serine/threonine protein kinase that is highly regulated at the transcriptional level by glucocorticoid hormones and suggests a novel interplay between glucocorticoid receptor signalling and a protein kinase of the second messenger family.

Characterization of sgk, a novel member of the serine/threonine protein kinase gene family which is transcriptionally induced by glucocorticoids and serum.

Study Objective:To determine the efficacy and toxicity of combination chemotherapy in patients with advanced, malignant pheochromocytoma. Design:Nonrandomized, single-arm trial. Setting:Go...

Malignant Pheochromocytoma: Effective Treatment with a Combination of Cyclophosphamide, Vincristine, and Dacarbazine

The evolution of genomic imprinting in mammals occurred more than 100 million years ago, and resulted in the formation of genes that are functionally haploid because of parent-of-origin–dependent expression. Despite ample evidence from studies in a number of species suggesting the presence of imprinted genes on human chromosome 14, their identity has remained elusive. Here we report the identification of two reciprocally imprinted genes, GTL2 and DLK1, which together define a novel imprinting cluster on human chromosome 14q32. The maternally expressed GTL2 (gene trap locus 2) gene encodes for a nontranslated RNA. DLK1 (delta, Drosophila, homolog-like 1) is a paternally expressed gene that encodes for a transmembrane protein containing six epidermal growth factor (EGF) repeat motifs closely related to those present in the delta/notch/serrate family of signaling molecules. The paternal expression, chromosomal localization, and biological function of DLK1 also make it a likely candidate gene for the callipyge phenotype in sheep. Many of the predicted structural and regulatory features of the DLK1/GTL2 domain are highly analogous to those implicated in IGF2/H19 imprint regulation, including two hemimethylated consensus binding sites for the vertebrate enhancer blocking protein, CTCF. These results provide evidence that a common mechanism and domain organization may be used for juxtapositioned, reciprocally imprinted genes.

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Novel Imprinted DLK1/GTL2 Domain on Human Chromosome 14 Contains Motifs that Mimic Those Implicated in IGF2/H19 Regulation

Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and appears to arise from developing striated muscle-forming cells. Since insulin-like growth factor II (IGF-II) is involved in normal muscle growth and maturation and elevated IGF-II mRNA levels have previously been reported in rhabdomyosarcomas, we have been studying the possible role of IGF-II in the unregulated growth and invasive potential of these embryonal tumors. In this study, we demonstrate that 13 of 14 rhabdomyosarcoma tumors express high levels of IGF-II mRNA relative to normal adult muscle and also express mRNA for the type I IGF receptors on their cell surface, the receptor thought to mediate the effects of IGF-II on muscle cells. We have established several rhabdomyosarcoma cell lines in mitogen-free media and demonstrate that these cells express type I IGF receptors on their cell surface and secrete IGF-II into the media. Exogenous IGF-II is able to stimulate cellular motility in these cell lines as assayed in a modified Boyden chamber. Finally, alpha IR-3, a type I receptor antagonist, inhibits the growth of these cell lines in serum-free media but does not inhibit IGF-II-induced motility of these cells. These data suggest that endogenously produced IGF-II functions as an autocrine growth and motility factor in many rhabdomyosarcoma tumors. The mitogenic actions of IGF-II are mediated through a domain of the type I IGF receptor that is blocked by alpha IR-3. IGF-II-induced motility may be mediated through an alternative signaling pathway.

http://cgd.aacrjournals.org/cgi/reprint/1/7/325.pdf

Insulin-like growth factor II acts as an autocrine growth and motility factor in human rhabdomyosarcoma tumors.

dlk, a putative mammalian homeotic gene differentially expressed in small cell lung carcinoma and neuroendocrine tumor cell line.

We constructed a human pheochromocytoma cDNA library and used differential hybridization to human pheochromocytoma and human neuroblastoma cDNA probes to isolate genes that are highly expressed in the adrenal medullary neuroendocrine tumor, pheochromocytoma, but not in the more immature embryonal tumor of adrenal medulla, neuroblastoma. Two cDNA clones, pG8 and pG2, were more highly expressed in normal and neoplastic chromaffin tissue than they are in neuroblastoma. Furthermore, they are expressed in a remarkably limited number of other human tumors or normal tissues. pG8 is highly expressed in medullary thyroid carcinoma, another tumor of neural crest origin, which can occur in association with pheochromocytoma in the multiple endocrine neoplasia type II syndrome. pG2 is highly expressed in the adrenal cortex, an endocrine gland thought to be embryologically unrelated to the neural crest-derived adrenal medulla. The expression of both pG8 and pG2 can be induced in human neuroblastoma cells with dexamethasone, suggesting a mechanism by which glucocorticoids may influence development of a neuroendocrine phenotype.

S B Baylin

Papers

Molecular markers of neuroendocrine development and evidence of environmental regulation