Search

Disruptor of telomeric silencing 1 (Dot1p) is an exquisitely conserved histone methyltransferase and is the sole enzyme responsible for H3K79 methylation in the budding yeast Saccharomyces cerevisiae. It has been shown to be highly phosphorylated in vivo; however, the upstream kinases that act on Dot1p are almost entirely unknown in yeast and all other eukaryotes. Here, we used in vitro and in vivo kinase discovery approaches to show that mitogen‐activated protein kinase HOG1 (Hog1p) is a bona fide kinase of the Dot1p methyltransferase. In vitro kinase assays showed that Hog1p phosphorylates Dot1p at multiple sites, including at several proline‐adjacent sites that are consistent with known Hog1p substrate preferences. The activity of Hog1p was specifically enhanced at these proline‐adjacent sites on Dot1p upon Hog1p activation by the osmostress‐responsive MAP kinase kinase PBS2 (Pbs2p). Genomic deletion of HOG1 reduced phosphorylation at specific sites on Dot1p in vivo, providing further evidence for Hog1p kinase activity on Dot1p in budding yeast cells. Phenotypic analysis of knockout and phosphosite mutant yeast strains revealed the importance of Hog1p‐catalysed phosphorylation of Dot1p for cellular responses to ultraviolet‐induced DNA damage. In mammalian systems, this kinase–substrate relationship was found to be conserved: human DOT1L (the ortholog of yeast Dot1p) can be phosphorylated by the proline‐directed kinase p38β (also known as MAPK11; the ortholog of yeast Hog1p) at multiple sites in vitro. Taken together, our findings establish Hog1p and p38β as newly identified upstream kinases of the Dot1p/DOT1L H3K79 methyltransferase enzymes in eukaryotes. [ABSTRACT FROM AUTHOR]

The post-translational regulation of aromatase has not been well characterized as compared with transcriptional regulation. Several studies of post-translational regulation have focused on decreases in catalytic activity following phosphorylation. We report here dual post-translational regulation of aromatase, at the catalytic activity and protein levels. Microsomal aromatase prepared from JEG-3 cells was rapidly inactivated and subsequently degraded in the presence of a cytosolic fraction with calcium, magnesium, and ATP. In a reconstituted system consisting of microsomal and cytosolic fractions, aromatase was protected from protein degradation by treatment with alkaline phosphatase, whereas degradation was enhanced by treatment with calcineurin inhibitors ( FK506 and cyclosporin A). Furthermore, aromatase was protected from degradation by treatment with kinase inhibitors, especially the calcium/calmodulin kinase inhibitors KN62 and KN93. Similarly to the reconstituted system, aromatase in cultured JEG-3 cells was protected from degradation by KN93, whereas FK503 increased degradation in the presence of cycloheximide, although cellular aromatase m RNA levels were unchanged by these reagents. Knockdown of calcineurin and calcium/calmodulin kinase II (Ca MKII) with small interfering RNAs resulted in a dose-dependent increase in aromatase degradation and protection from degradation, respectively. The cytosol fraction-dependent phosphorylation of microsomal aromatase was inhibited by calcineurin, KN62, and KN93, and promoted by Ca MKII and FK506. These results indicate that aromatase is regulated acutely at the catalytic activity level and subsequently at the enzyme content level by Ca MKII/calcineurin-dependent phosphorylation/dephosphorylation. [ABSTRACT FROM AUTHOR]

One of the important determinants of virulence of Mycobacterium tuberculosis is adaptation to adverse conditions encountered in the host cells. The ability of Mycobacterium to successfully adapt to stress conditions is brought about by the expression of specific regulons effected by a repertoire of σ factors. The induction and availability of σ factors in response to specific stimuli is governed by a complex regulatory network comprising a number of proteins, including σ factors themselves. A serine–threonine protein kinase-mediated signaling pathway adds another dimension to the mycobacterial σ factor regulatory network. This review highlights the recent advances in understanding mycobacterial σ factors, their regulation and contribution to bacterial pathogenesis. [ABSTRACT FROM AUTHOR]

Death-associated protein kinase (DAPK) is a pro-apoptotic serine/threonine protein kinase that is dysregulated in a wide variety of cancers. The mechanism by which this occurs has largely been attributed to promoter hypermethylation, which results in gene silencing. However, recent studies indicate that DAPK expression can be detected in some cancers, but its function is still repressed, suggesting that DAPK activity can be subverted at a post-translational level in cancer cells. This review will focus on recent data describing potential mechanisms that may alter the expression, regulation or function of DAPK. [ABSTRACT FROM AUTHOR]