Search

ABSTRACTIgf2bp1 is an oncofetal RNA binding protein whose expression in numerous types of cancers is associated with upregulation of key pro-oncogenic RNAs, poor prognosis, and reduced survival. Importantly, Igf2bp1 synergizes with mutations in Kras to enhance signalling and oncogenic activity, suggesting that molecules inhibiting Igf2bp1 could have therapeutic potential. Here, we isolate a small molecule that interacts with a hydrophobic surface at the boundary of Igf2bp1 KH3 and KH4 domains, and inhibits binding to Kras RNA. In cells, the compound reduces the level of Kras and other Igf2bp1 mRNA targets, lowers Kras protein, and inhibits downstream signalling, wound healing, and growth in soft agar, all in the absence of any toxicity. This work presents an avenue for improving the prognosis of Igf2bp1-expressing tumours in lung, and potentially other, cancer(s).

There are two vertebrate nonmuscle myosin heavy chain (MHC) genes that encode two separate isoforms of the heavy chain, MHC-A and MHC-B. Recent work has identified additional, alternatively spliced isoforms of MHC-B cDNA with inserted sequences of 30 nucleotides (chicken and human) or 48 nucleotides (Xenopus) at a site corresponding to the ATP binding region in the MHC protein (Takahashi, M., Kawamoto, S., and Adelstein, R. S.(1992) J. Biol. Chem.267, 17864-17871) and Bhatia-Dey, N., Adelstein, R. S., and Dawid, I. B. (1993) Proc. Natl. Acad. Sci. U. S. A.90, 2856-2859). The deduced amino acid sequence of these inserts contains a consensus sequence for phosphorylation by cyclin-p34cdc2 (cdc2) kinase. In cultured XenopusXTC cells, we have identified two inserted MHC-B isoforms and a noninserted MHC-A isoform by immunoblotting of cell extracts. When myosin was immunoprecipitated from XTC cells and phosphorylated in vitrowith cdc2 kinase, the kinase catalyzed the phosphorylation of both inserted MHC-B isoforms but not MHC-A. Isoelectric focusing of tryptic peptides generated from MHC-B phosphorylated with cdc2 kinase revealed one major phosphopeptide that was purified by reverse-phase high performance liquid chromatography and sequenced. The phosphorylated residue was Ser-214, the cdc2 kinase consensus site within the insert near the ATP binding region. The same site was phosphorylated in intact XTC cells during log phase of growth and in cell-free lysates of Xenopuseggs stabilized in second meiotic metaphase but not interphase. Moreover, Ser-214 phosphorylation was detected during maturation of Xenopusoocytes when the cdc2 kinase-containing maturation-promoting factor was activated, but not in G2interphase-arrested oocytes. These results demonstrate that MHC-B phosphorylation is tightly regulated by cdc2 kinase during meiotic cell cycles. Furthermore, MHC-A and MHC-B isoforms are differentially phosphorylated at these stages, suggesting that they may serve different functions in these cells.