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Methanococcus maripaludis is an archaeon with two studied surface appendages, archaella and type IV-like pili. Previously, the major structural pilin was identified as MMP1685 and three additional proteins were designated as minor pilins (EpdA, EpdB and EpdC). All of the proteins are likely processed by the pilin-specific prepilin peptidase EppA. Six other genes were identified earlier as likely encoding pilin proteins processed also by EppA. In this study, each of the six genes (mmp0528, mmp0600, mmp0601, mmp0709, mmp0903 and mmp1283) was deleted and the mutants examined by electron microscopy to determine their essentiality for pili formation. While mRNA transcripts of all genes were detected by RT-PCR, only the deletion of mmp1283 led to nonpiliated cells. This strain could be complemented back to a piliated state by supplying a wildtype copy of the mmp1283 gene in trans. This study adds to the complexity of the type IV pili system in M. maripaludis and raises questions about the functions of the remaining five pilin-like genes and whether M. maripaludis under other growth conditions may be able to assemble additional pili-like structures. [ABSTRACT FROM AUTHOR]

Methanococcus maripaludis is an archaeon with two studied surface appendages, archaella and type IV-like pili. Previously, the major structural pilin was identified as MMP1685 and three additional proteins were designated as minor pilins (EpdA, EpdB and EpdC). All of the proteins are likely processed by the pilin-specific prepilin peptidase EppA. Six other genes were identified earlier as likely encoding pilin proteins processed also by EppA. In this study, each of the six genes (mmp0528, mmp0600, mmp0601, mmp0709, mmp0903 and mmp1283) was deleted and the mutants examined by electron microscopy to determine their essentiality for pili formation. While mRNA transcripts of all genes were detected by RT-PCR, only the deletion of mmp1283 led to nonpiliated cells. This strain could be complemented back to a piliated state by supplying a wildtype copy of the mmp1283 gene in trans. This study adds to the complexity of the type IV pili system in M. maripaludis and raises questions about the functions of the remaining five pilin-like genes and whether M. maripaludis under other growth conditions may be able to assemble additional pili-like structures. [ABSTRACT FROM AUTHOR]

The KRAS proto-oncogene plays a key role in the development of many human tumors and is commonly activated by somatic mutation or signaling through specific growth factor receptors. However, the interaction between the microenvironment and K-ras activity has not been defined. Hypoxia invariably develops as tumors outgrow their supply of oxygen. A series of well-orchestrated cellular adaptations occur that stimulate angiogenesis and enhance survival of the tumor in hypoxic conditions. Our previous studies demonstrated that mutant KRAS alleles can interact with hypoxia to induce vascular endothelial growth factor (VEGF) in colon cancer. We sought to determine whether similar hypoxic responses are also present in tumors without a KRAS mutation. Hypoxia consistently increased the levels of activated, GTPbound K-ras in colon cancer cell lines with a wild-type KRAS gene, and this depended upon the activation of c-Src. Inhibition of c-Src by PP2 treatment or siRNA knockdown blocked the hypoxic activation of K-ras. This activation of K-ras did not depend upon EGFR and resulted in the phosphorylation of Akt and induction of VEGF expression. In addition, activation of K-ras significantly blocked apoptosis in hypoxic conditions. These studies reveal a unique adaptive mechanism in hypoxia that activates K-ras signaling in the absence of a mutant KRAS oncogene. [ABSTRACT FROM AUTHOR]