Identification of mRNAs associated with alphaCP2-containing RNP complexes.

Posttranscriptional controls in higher eukaryotes are central to cell differentiation and developmental programs. These controls reflect sequence-specific interactions of mRNAs with one or more RNA binding proteins. The alpha-globin poly(C) binding proteins (alphaCPs) comprise a highly abundant subset of K homology (KH) domain RNA binding proteins and have a characteristic preference for binding single-stranded C-rich motifs. alphaCPs have been implicated in translation control and stabilization of multiple cellular and viral mRNAs. To explore the full contribution of alphaCPs to cell function, we have identified a set of mRNAs that associate in vivo with the major alphaCP2 isoforms. One hundred sixty mRNA species were consistently identified in three independent analyses of alphaCP2-RNP complexes immunopurified from a human hematopoietic cell line (K562). These mRNAs could be grouped into subsets encoding cytoskeletal components, transcription factors, proto-oncogenes, and cell signaling factors. Two mRNAs were linked to ceroid lipofuscinosis, indicating a potential role for alphaCP2 in this infantile neurodegenerative disease. Surprisingly, alphaCP2 mRNA itself was represented in alphaCP2-RNP complexes, suggesting autoregulatory control of alphaCP2 expression. In vitro analyses of representative target mRNAs confirmed direct binding of alphaCP2 within their 3' untranslated regions. These data expand the list of mRNAs that associate with alphaCP2 in vivo and establish a foundation for modeling its role in coordinating pathways of posttranscriptional gene regulation.