[Abstract unavailable

A molecular clone corresponding to a 1.2-kilobase mRNA enriched in Rous sarcoma virus-transformed chicken embryo fibroblasts (CEF) was identified by differential screening of a cDNA library. The induction of the cloned sequence (denoted pCEF-4) in CEF infected by the temperature-sensitive mutant NY72-4 Rous sarcoma virus is rapid and independent of protein synthesis. DNA sequencing of the 1.2-kilobase insert of CEF4 revealed an open reading frame that predicts an 11-kDa protein. The predicted pCEF-4 gene product is homologous to human connective tissue-activating peptide III (CTAP-Il) and platelet factor 4 (PF-4). Serum stimulation of quiescent normal CEF results in a rapid but transient expression ofpCEF-4 mRNA. Hence, pCEF-4 mRNA is expressed at the G.-G1 transition and during the first G, phase of normal CEF reentering the cell cycle. The expression of pCEF-4 mRNA in Rous sarcoma virus-transformed CEF appears to be the result of transcriptional activation and stabilization of the transcript.Much of our knowledge of the gene products responsible for cell transformation is derived from investigations of the virally encoded oncogenes and of the protooncogenes, their cellular ancestors. Functional and structural similarities often exist between oncogene products and growth factors, growth factor receptors, or the products of other genes expressed during the normal mitogenic response (1). In several instances, the alteration in cellular protooncogenes resulting in their oncogenic activation is understood (1-4). Hence, considerable progress has been accomplished regarding the biochemical characterization of some of the agents that cause cell transformation. In contrast, little is known about the biochemical pathways and cellular activities critically modified during the transformation process. The absence of functional assays and the lack of an appropriate model system amenable to genetic manipulation have clearly limited our progress in this respect. Various approaches have been utilized to circumvent these limitations. One involves the study of protein phosphorylation in normal and transformed cells, because a class of transforming proteins exhibits tyrosine-specific kinase activity. Some investigators have also compared the role of protooncogenes in normal and malignant growth because of the obvious links between this class of genes and the mitogenic response. We have followed a third approach by searching for genes repressed or expressed in response to transforming proteins or growth factors without regard to their possible relationship to known oncogenes.In this report, we describe a cDNA clone (denoted pCEF-4) corresponding to a 1.2-kilobase (kb) mRNA species that is expressed transiently in response to serum and constitutively in Rous sarcoma virus (RSV)-transformed chicken embryo fibroblasts (CEF) in the presence or absence of serum. Increased transcription and stabilization result in the accumulation of the pCEF-4 mRNA in RSV-transformed cells. A polypeptide of Mr 11,000 is predicted by the nucleic...

The role of activating protein-1 (AP-1) in muscle cells is currently equivocal. While some studies propose that AP-1 is inhibitory for myogenesis, others implicate a positive role in this process. We tested whether this variation may be due to different properties of the AP-1 subunit composition in differentiating cells. Using Western analysis we show that c-Jun, Fra-2, and JunD are expressed throughout the time course of differentiation. Phosphatase assays indicate that JunD and Fra-2 are phosphorylated in muscle cells and that at least two isoforms of each are expressed in muscle cells. Electrophoretic mobility shift assays combined with antibody supershifts indicate the appearance of Fra-2 as a major component of the AP-1 DNA binding complex in differentiating cells. In this context it appears that Fra-2 heterodimerizes with c-Jun and JunD. Studying the c-jun enhancer in reporter gene assays we observed that the muscle transcription factors MEF2A and MyoD can contribute to robust transcriptional activation of the c-jun enhancer. In differentiating muscle cells mutation of the MEF2 site reduces transactivation of the c-jun enhancer and MEF2A is the predominant MEF2 isoform binding to this cis element. Transcriptional activation of an AP-1 site containing reporter gene (TRE-Luc) is enhanced under differentiation conditions compared with growth conditions in C2C12 muscle cells. Further studies indicate that Fra-2 containing AP-1 complexes can transactivate the MyoD enhancer/promoter. Thus, an AP-1 complex containing Fra-2 and c-Jun or JunD is consistent with muscle differentiation, indicating that AP-1 function during myogenesis is dependent on its subunit composition.

Menin, the product of the multiple endocrine neoplasia type I gene, has been implicated in several biological processes, including the control of gene expression and apoptosis, the modulation of mitogen-activated protein kinase pathways, and DNA damage sensing or repair. In this study, we have investigated the function of menin in the model organism Drosophila melanogaster. We show that Drosophila lines overexpressing menin or an RNA interference for this gene develop normally but are impaired in their response to several stresses, including heat shock, hypoxia, hyperosmolarity and oxidative stress. In the embryo subjected to heat shock, this impairment was characterized by a high degree of developmental arrest and lethality. The overexpression of menin enhanced the expression of HSP70 in embryos and interfered with its down-regulation during recovery at the normal temperature. In contrast, the inhibition of menin with RNA interference reduced the induction of HSP70 and blocked the activation of HSP23 upon heat shock, Menin was recruited to the Hsp70 promoter upon heat shock and menin overexpression stimulated the activity of this promoter in embryos. A 70-kDa inducible form of menin was expressed in response to heat shock, indicating that menin is also regulated in conditions of stress. The induction of HSP70 and HSP23 was markedly reduced or absent in mutant embryos harboring a deletion of the menin gene. These embryos, which did not express the heat shock-inducible form of menin, were also hypersensitive to various conditions of stress. These results suggest a novel role for menin in the control of the stress response and in processes associated with the maintenance of protein integrity.

We isolated a cDNA for p20K, a secreted protein preferentially synthesized in nonproliferating cells. p20K mRNA and protein levels declined rapidly following treatment with various mitogens. DNA sequence analysis of the p20K cDNA predicted a novel protein distantly related to alpha 2 mu-globulin and plasma retinol-binding protein.