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HMGI-C is a nuclear architectural factor which is expressed during embryogenesis but not in adult tissues while it becomes re-expressed following neoplastic transformation. In this paper we identify the promoter region of the mouse Hmgi-c gene and by stepwise deletion of the 5' sequences we map the promoter activity of the most abundant transcript to a very short fragment containing a long polypyrimidine/polypurine (ppyr/ppur) tract. We demonstrate that this tract is a multiple binding site for the transcription factors Sp1 and Sp3 and that in Drosophila SL2 cells, Spl activates the Hmgi-c promoter. In addition, another transcription factor, CTF/NF-1, binds the proximal promoter immediately downstream of this region and its mutation decreases transcription in NIH-3T3 cells. This study identifies factors responsible for the basal activity of Hmgi-c gene and provides a foundation for further analysis of the mechanism of its regulation.

The RET proto-oncogene encodes a tyrosine-kinase receptor specifically expressed in tissues of neuroectodermal origin. Recently specific point mutations of RET have been demonstrated to be responsible for the Multiple Endocrine Neoplasia type 2A and 2B and Familial Medullary Thyroid Carcinoma syndromes, characterized by the occurrence of medullary thyroid carcinomas. Here we report that a human medullary thyroid carcinoma cell line, the TT cell line, harbours a MEN2A-type mutation, specifically a cysteine to triptophan substitution at the level of the RET codon 634. This mutation is heterozygous and both normal and mutated alleles are expressed. We suggest that the TT cell line could be a useful cell system to investigate the role played by the RET oncogene in the transformation and differentiation of human thyroid C-cells.

Both cytoplasmic and membrane-bound protein kinase C activities are increased in: Harvey-Sarcoma Virus, infected thyroid epithelial cells. The cytoplasmic kinase C increase is found in the chromatographic fraction eluted at lower salt concentration (100 mM NaCl-S100), while the more acidic protein fraction eluted at higher salt concentration (350 mM NaCl-S350) is virtually absent. Although the cytoplasmic S100 fraction from the control and ras-virus infected cells display a comparable PBt2 binding activity, they are different in the Ca+2-dependence and the TPA down regulation. In addition, the membranes from the control and ras-virus infected cells are different phosphate acceptors in place of the Hl histones. © 1988 Academic Press, Inc.

The activity of the adenylate cyclase catalytic subunit is higher in Harvey and Kirsten Murine Sarcoma Viruses-infected thyroid epithelial cells than in uninfected control cells either in the presence of Mg2+ alone or following stimulation by Mn2+ or forskolin. The higher activity is associated with an increased cAMP cellular content. The Gpp(NH)p and F- anion are more effective positive modulators in the control than in the virus infected cells: these results exclude therefore that the ras p21 proteins can act as the G-protein alpha-subunit and suggest that they negatively interfere with the G-protein modulation of the adenylate cyclase system. The activity of the adenylate cyclase catalytic subunit is higher in Harvey and Kirsten Murine Sarcoma Viruses-infected thyroid epithelial cells than in uninfected control cells either in the presence of Mg2+ alone or following stimulation by Mn2+ or forskolin. The higher activity is associated with an increased cAMP cellular content. The Gpp(NH)p and F- anion are more effective positive modulators in the control than in the virus infected cells: these results exclude therefore that the ras p21 proteins can act as the G-protein alpha-subunit and suggest that they negatively interfere with the G-protein modulation of the adenylate cyclase system. © 1987.