Distant homologs of anti-apoptotic factor HAX1 encode parvalbumin-like calcium binding proteins

<p>Abstract</p> <p>Background</p> <p>Apoptosis is a highly ordered and orchestrated multiphase process controlled by the numerous cellular and extra-cellular signals, which executes the programmed cell death <it>via </it>release of cytochrome c alterations in calcium signaling, caspase-dependent limited proteolysis and DNA fragmentation. Besides the general modifiers of apoptosis, several tissue-specific regulators of this process were identified including HAX1 (HS-1 associated protein X-1) - an anti-apoptotic factor active in myeloid cells. Although HAX1 was the subject of various experimental studies, the mechanisms of its action and a functional link connected with the regulation of apoptosis still remains highly speculative.</p> <p>Findings</p> <p>Here we provide the data which suggests that HAX1 may act as a regulator or as a sensor of calcium. On the basis of iterative similarity searches, we identified a set of distant homologs of HAX1 in insects. The applied fold recognition protocol gives us strong evidence that the distant insects' homologs of HAX1 are novel parvalbumin-like calcium binding proteins. Although the whole three EF-hands fold is not preserved in vertebrate our analysis suggests that there is an existence of a potential single EF-hand calcium binding site in HAX1. The molecular mechanism of its action remains to be identified, but the risen hypothesis easily translates into previously reported lines of various data on the HAX1 biology as well as, provides us a direct link to the regulation of apoptosis. Moreover, we also report that other family of myeloid specific apoptosis regulators - myeloid leukemia factors (MLF1, MLF2) share the homologous C-terminal domain and taxonomic distribution with HAX1.</p> <p>Conclusions</p> <p>Performed structural and active sites analyses gave new insights into mechanisms of HAX1 and MLF families in apoptosis process and suggested possible role of HAX1 in calcium-binding, still the analyses require further experimental verification.</p

Unexpected domain composition of MACC1 links MET signaling and apoptosis

Colorectal cancer, one of the most challenging malignancies, still has a limited number of recognized prognostic and predictive markers indicating appropriate treatment. MACC1 (metastasis-associated in colon cancer-1), a novel regulator of tumor growth and metastasis has recently been identified as an important prognostic factor of metastatic disease in colorectal cancer. The mechanism of MACC1 activity remains undetermined. Here we apply a combination of fold recognition and homology modeling algorithms to draft MACC1 function. The applied methods revealed that the MACC1 protein consists of four domains: ZU5, SH3, and two C-terminal death domains (DD). Previously a similar domain architecture (ZU5-DD) was observed in other proteins, involved mainly in signal transduction and apoptosis regulation. Based on the specific aspects of the closest homologues' biology functional hypotheses on MACC1 are proposed. A broad range of bioinformatic analyzes indicates that MACC1, besides its involvement in signal transduction from the MET receptor, links MET signaling and apoptosis