Activation of oncogenic signaling kinase PAK1 by ionising radiation confers an aggressive phenotype in head and neck squamous cell carcinoma.

Head and neck squamous cancers are very aggressive tumors often diagnosed in late stages with poor prognosis. HNSCCs are usually treated by a course of radiation (IR) therapy and followed by surgery. These treatment regimens fail to bring a complete response. Molecular signatures in tumors are attributed to this response and an improved understanding of the signaling events could offer new avenues for therapy. Here, we show that P21 activated kinase-1 (PAK1) - an oncogenic signaling serine/threonine kinase, is activated upon exposure to IR and this leads to an accelerated tumorigenic character in HNSCC cells. Our results show that PAK1 is highly expressed in HNSCC cell lines, as compared to normal buccal mucosa cells and when HNSCC cells were exposed to IR, they show activated PAK1 and an aggressive phenotype as determined by in vitro functional assays. PAK1 levels were elevated in HNSCC as compared to adjacent normal oral tissues and our results also show convincing evidence of activated PAK1 in patient tumor samples of post- IR treatment as compared to pre-IR treatment and is associated with poor survival. Pak1 Knockout (KO) clones in HNSCC cells showed that they were more sensitive to IR as compared to wild type (wt) cells. This altered sensitivity to IR was attributed to enhanced DNA damage response modulated by PAK1 in cells. Overall, our results suggest that PAK1 expression in HNSCC could be a critical determinant in IR therapy response and silencing PAK1 is likely to be a treatment modality to improve clinical outcomes.

A novel meta-cleavage product hydrolase from Flavobacterium sp. ATCC27551.

The organophosphate degrading (opd) gene cluster of plasmid pPDL2 of Flavobacterium sp. ATCC27551 contains a novel open-reading frame, orf243. This was predicted to encode an alpha/beta hydrolase distantly related to the meta-fission product (MFP) hydrolases such as XylF, PhnD, and CumD. By homology modeling Orf243 has most of the structural features of MFP hydrolases including the characteristic active site catalytic triad. The purified protein (designated MfhA) is a homotetramer and shows similar affinity for 2-hydroxy-6-oxohepta-2,4-dienoate (HOHD), 2-hydroxymuconic semialdehyde (HMSA), and 2-hydroxy-5-methylmuconic semialdehyde (HMMSA), the meta-fission products of 3-methyl catechol, catechol, and 4-methyl catechol. The unique catalytic properties of MfhA and the presence near its structural gene of cis-elements required for transposition suggest that mfhA has evolved towards encoding a common hydrolase that can act on meta-fission products containing either aldehyde or ketone groups.