Regulation of transcription factor AP-2 by the morphogen retinoic acid and by second messengers

Multifactorial control of insulin receptor gene expression in human cell lines

Taking advantage of a computer program to align DNA sequences we scanned the 5'-flanking region of the insulin receptor gene to localize putative regulatory elements. Using this approach as a start point, we investigated the effect of several agents on insulin receptor gene expression in human cells. We found that (i) forskolin reduces insulin receptor mRNA levels; (ii) the effects of either forskolin or dexamethasone on insulin receptor mRNA levels are near completely abolished in glucose-starved cells; (iii) 2-mercaptoethanol and heat shock, besides previously described stress conditions (glycosylatyon inhibitors), reduce insulin receptor mRNA levels.

A candidate protein kinase C gene, PKC1, is required for the S. cerevisiae cell cycle

Probes derived from cDNAs encoding isozymes of rat protein kinase C (PKC) were used to screen the genome of the budding yeast S. cerevisiae. A single gene (PKC1) was isolated that encodes a putative protein kinase closely related to the alpha, beta, and gamma subspecies of mammalian PKC. Deletion of PKC1 resulted in recessive lethality. Cells depleted of the PKC1 gene product displayed a uniform phenotype, a characteristic of cell division cycle (cdc) mutants, and arrested cell division at a point subsequent to DNA replication, but prior to mitosis. Unlike most cdc mutants, which continue to grow in the absence of cell division, PKC1-depleted cells arrested growth with small buds. PKC1 may regulate a previously unrecognized checkpoint in the cell cycle.

Identification of a retinoic acid-sensitive period during primary axis formation in Xenopus laevis

Retinoic acid (RA) is able to profoundly alter patterning of the primary body axis in embryos of the frog Xenopus laevis. The response to RA is dose-dependent, and leads to progressive truncation of the anteroposterior axis, with anterior structures most sensitive. Both mesodermal and ectodermal tissues are affected, and in vitro assays demonstrate that induced dorsal ectoderm is one direct target of RA. RA represses expression of anterior-specific genes and concomitantly induces expression of at least one posterior-specific gene. Resistance to RA is acquired gradually, during gastrula and early neurula stages, with posterior structures becoming resistant before anterior structures. These data demarcate in the embryo an anterior "domain," which may define the head rudiment and which transcends germ layers. RA can alter the axial pattern after its initial induction; thus, RA sensitivity defines a labile intermediate that occurs during axial patterning. These data suggest a possible role for RA in normal axis formation.

Regulation of gene expression by tumor promoters

Tumor promoters change the program of genes expressed in cells in culture and in the multicellular organism. The growing list of genes that are induced or repressed includes protooncogenes, transcription factors, secreted proteases and viruses. Most of the regulation is at the level of transcription. Several of the cis-acting promoter elements mediating regulation, the transcription factors binding to these elements and their post-translational activation, as well as some of the initial steps of the interaction of cells with tumor promoters have been characterized. The components of the signal transduction chain to the nucleus are, however, still unknown. Mutant and inhibitor studies suggest that the activation or inactivation of certain genes constitute the basis for the development of the tumor promotion phenotype.