Inactivation of myocardin and p16 during malignant transformation contributes to a differentiation defect.

Myocardin is known as an important transcriptional regulator in smooth and cardiac muscle development. Here we found that myocardin is frequently repressed during human malignant transformation, contributing to a differentiation defect. We demonstrate that myocardin is a transcriptional target of TGFbeta required for TGFbeta-mediated differentiation of human fibroblasts. Serum deprivation, intact contact inhibition response, and the p16ink4a/Rb pathway contribute to myocardin induction and differentiation. Restoration of myocardin expression in sarcoma cells results in differentiation and inhibition of malignant growth, whereas inactivation of myocardin in normal fibroblasts increases their proliferative potential. Myocardin expression is reduced in multiple types of human tumors. Collectively, our results demonstrate that myocardin is an important suppressive modifier of the malignant transformation process.

Is the G72/G30 locus associated with schizophrenia? single nucleotide polymorphisms, haplotypes, and gene expression analysis.

BACKGROUND: The genes G72/G30 were recently implicated in schizophrenia in both Canadian and Russian populations. We hypothesized that 1) polymorphic changes in this gene region might be associated with schizophrenia in the Ashkenazi Jewish population and that 2) changes in G72/G30 gene expression might be expected in schizophrenic patients compared with control subjects. METHODS: Eleven single nucleotide polymorphisms (SNPs) encompassing the G72/G30 genes were typed in the genomic deoxyribonucleic acid (DNA) from 60 schizophrenic patients and 130 matched control subjects of Ashkenazi ethnic origin. Case-control comparisons were based on linkage disequilibrium (LD) and haplotype frequency estimations. Gene expression analysis of G72 and G30 was performed on 88 postmortem dorsolateral prefrontal cortex samples. RESULTS: Linkage disequilibrium analysis revealed two main SNP blocks. Haplotype analysis on block II, containing three SNPs external to the genes, demonstrated an association with schizophrenia. Gene expression analysis exhibited correlations between expression levels of the G72 and G30 genes, as well as a tendency toward overexpression of the G72 gene in schizophrenic brain samples of 44 schizophrenic patients compared with 44 control subjects. CONCLUSIONS: It is likely that the G72/G30 region is involved in susceptibility to schizophrenia in the Ashkenazi population. The elevation in expression of the G72 gene coincides with the glutamatergic theory of schizophrenia.

Myocardin in tumor suppression and myofibroblast differentiation.

The malignant transformation process is associated with defects in cell cycle regulation and disruption of the normal differentiation programs in both neoplastic and adjacent stroma cells. However, the relationships between the cell cycle, differentiation and cancer are very complex and tissue specific. Recently we have demonstrated a previously unrecognized role in human carcinogenesis for the important regulator of cardiac and smooth muscle differentiation, myocardin. Myocardin expression is frequently repressed during human malignant transformation contributing to a differentiation defect in the premalignant mesenchymal cells. TGFbeta treatment, serum deprivation and intact contact inhibition response all contribute to myocardin induction and differentiation. Positive regulation of myocardin mRNA levels and activity by the p16/Rb pathway provides a molecular link between cell cycle and differentiation defects during cancer development. In addition, we show that myocardin represses its own expression in human fibroblasts. This negative autoregulatory loop might be potentially important for restraining myocardin activity and allowing reversibility of fibroblast-myofibroblast phenotypic conversion. Here we discuss the emerging role of myocardin in tumor suppression as well as novel aspects of its regulation in normal and malignant conditions.

A novel protein derived from the MUC1 gene by alternative splicing and frameshifting.

Genes that have been designated the name "MUC" code for proteins comprising mucin domains. These proteins may be involved in barrier and protective functions. The first such gene to be characterized and sequenced is the MUC1 gene. Here we report a novel small protein derived from the MUC1 gene by alternative splicing that does not contain the hallmark of mucin proteins, the mucin domain. This protein termed MUC1/ZD retains the same N-terminal MUC1 sequences as all of the other known MUC1 protein isoforms. The common N-terminal sequences comprise the signal peptide and a subsequent stretch of 30 amino acids. In contrast, the MUC1/ZD C-terminal 43 amino acids are novel and result from a reading frameshift engendered by a splicing event that forms MUC1/ZD. The expression of MUC1/ZD at the protein level in human tissues is demonstrated by Western blotting, immunohistochemistry, immunoprecipitation, and an ELISA. Utilization was made of affinity-purified MUC1/ZD-specific polyclonal antibodies as well as two different monoclonal antibodies that are monospecific for the MUC1/ZD protein. The MUC1/ZD protein is expressed in tissues as an oligomeric complex composed of monomers linked by disulfide bonds contributed by MUC1/ZD cysteine residues. MUC1/ZD protein expression did not parallel that of the tandem-repeat array-containing MUC1 protein. Results presented here demonstrate for the first time the expression of a novel MUC1 protein isoform MUC1/ZD, which is generated by an alternative splicing event that both deletes the tandem-repeat array and leads to a C-terminal reading frameshift.