Characterization of rat BLOS2/Ceap, a putative yeast She3 homolog, as interaction partner of apoptosis antagonizing transcription factor/Che-1.

AATF/Che-1 is a coactivator of several transcription factors, including steroid hormone receptors. In search of novel interaction partners of AATF, we identified BLOS2 (BLOC1S2, also termed Ceap) from a rat cDNA library. BLOS2 is extremely conserved with a high degree of homology to yeast She3p. The clone isolated represents a splice variant encoding a polypeptide of 168 residues. Rat BLOS2 mRNA is highly expressed in brain and testis and at lower levels in other tissues, but not in skeletal or smooth muscle. Expression as a tagged fusion protein revealed predominant cytoplasmic, but also nuclear localization. In the cytoplasm, BLOS2 fusion proteins exhibit diffuse, filamentous, or dotted distribution, with the latter partially co-localizing with recycling endosomes. In addition, BLOS2 localizes to centrosomes or the pericentrosomal region. Moreover, BLOS2 co-localizes with myosin V globular tail domains in vesicle-like structures. However, a direct interaction could not be demonstrated. In transactivation assays, BLOS2 enhanced transcription from androgen receptor and p53-responsive promoters. However, this enhancement correlated with accumulation of both androgen receptor and p53, suggesting that BLOS2 has a stabilizing effect on these transcription factors. We propose that BLOS2 functions as an adapter in processes such as protein and vesicle processing and transport, and perhaps transcription.