PCBP4 blocking peptide

The mechanisms through which iron-dependent enzymes receive their metal cofactors are largely unknown. Poly r(C)-binding protein 1 (PCBP1) is an iron chaperone for ferritin; both PCBP1 and its paralog PCBP2 are required for iron delivery to the prolyl hydroxylase that regulates HIF1. Here we show that PCBP2 is also an iron chaperone for ferritin. Co-expression of PCBP2 and human ferritins in yeast activated the iron deficiency response and increased iron deposition into ferritin. Depletion of PCBP2 in Huh7 cells diminished iron incorporation into ferritin. Both PCBP1 and PCBP2 were co-immunoprecipitated with ferritin in HEK293 cells, and expression of both PCBPs was required for ferritin complex formation in cells. PCBP1 and -2 exhibited high affinity binding to ferritin in vitro. Mammalian genomes encode 4 PCBPs, including the minimally expressed PCBPs 3 and 4. Expression of PCBP3 and -4 in yeast activated the iron deficiency response, but only PCBP3 exhibited strong interactions with ferritin. Expression of PCBP1 and ferritin in an iron-sensitive, ccc1 yeast strain intensified the toxic effects of iron, whereas expression of PCBP4 protected the cells from iron toxicity. Thus, PCBP1 and -2 form a complex for iron delivery to ferritin, and all PCBPs may share iron chaperone activity.

The protein alpha CP-4 (also known as hnRNP E4) is an RNA binding protein encoded by a gene at 3p21, one of the most common altered regions in lung cancer. It has been proposed that aCP-4 may function as a lung tumor suppressor. Lack of aCP-4 expression is frequent in highly proliferative lung tumors and correlates with alpha CP-4 allele losses. The aim of this study was to evaluate the effect of aCP-4 on the tumorigenic capacity of lung cancer cells. aCP-4 expression was induced by transient transfection or stable infection with recombinant retroviruses. Induction of aCP-4 expression caused cell cycle arrest in G(2)/M in 3 out of the 7 lung cancer cell lines studied, while no effect on apoptosis was observed. Anchorage-independent growth and invasion capacity of H1299 cells were significantly reduced by alpha CP-4 induction. Tumorigenicity of H1299 cells in nude mice was greatly inhibited by the expression of aCP-4. Moreover, induction of aCP-4 expression in already established tumors resulted in a sudden growth arrest. Immunocytochemistry analysis of the xenograft tumors revealed an in vivo effect of aCP-4 on cell proliferation and no effect on apoptosis. Finally, alpha CP-4 showed a subcellular localization different from alpha CP-4a, a splice variant that does not affect cell proliferation. In conclusion, expression of alpha CP-4 can inhibit proliferation and tumorigenesis of lung cancer cells, both in vivo and in vitro, by delaying the progression of the cell cycle. (c) 2007 Wiley-Liss, Inc.