SPIN1 is necessary for normal meiotic progression in mammals. It is overexpressed in human ovarian cancers and some cancer cell lines. Here, we examined the functional significance and regulation of SPIN1 and SPIN3 in the TCam-2 human seminoma cell line. We found that while SPIN1 overexpression reduced apoptosis in these cells, SPIN3 overexpression induced it. Similarly, SPIN1 upregulated and SPIN3 downregulated CYCD1, which is a downstream target of the PI3K/AKT pathway and contributes to apoptosis resistance in cancer cell lines. It appears that SPIN1 is pro-oncogenic and SPIN3 acts as a tumor suppressor in TCam-2 cells. To our knowledge, this is the first report of SPIN3 tumor suppressor activity. However, both SPIN1 and SPIN3 stimulated cell cycle progression. In addition, using luciferase reporters carrying SPIN1 or SPIN3 mRNA 3′UTRs, we found that PUM1 and PUM2 targeted and repressed SPINs. We also found that PUM1 itself strongly stimulated apoptosis and moderately slowed cell cycle progression in TCam-2 cells, suggesting that PUM1, like SPIN3, is a tumor suppressor. Our findings suggest that acting, at least in part, through SPIN1 and SPIN3, PUM proteins contribute to a mechanism promoting normal human male germ cell apoptotic status and thus preventing cancer.

Materials and Methods Semi-quantitative RT-PCRFor RT-PCR, after transfection of MCF-7 cells with siRNA or DNA plasmids and treatment with specific stress agents, total RNA was isolated from the cells using TriReagent (Molecular Research Centre, Inc.) according to the manufacturer's protocol. RT-PCR was performed as previously described [10]. Briefly, the cDNA was prepared from 200 ng of RNA using 100 ng of oligo(dT)18 primer and 100 units of SuperScript TM III reverse transcriptase (Invitrogen). Equal volumes of cDNA were used to amplify DNA fragments of hnRNP K and ß-actin using the following primers: hnRNP K Forward: 5′-CCTATGACAGAAGAGGGAGAC-3′; hnRNP K Reverse: 5′-CCCTGTGGTTCATAAGCCATC-3′; ß-actin Forward: 5′-AGAGCAAGAGAGGCATCCTG-3′; ßactin Reverse: 5′-CGACGTAGCACAGCTTCTCC-3′.

In this review, the latest research concerning the structure and function of the 5′-terminal region of p53 mRNA was discussed. Special attention was focused on defined structural motifs which are present in this region, as well as their conservation and plausible functional role in translation. It is known that the length of the 5′-terminal region and the structural environment of initiation codons can strongly modulate translation initiation. The ability of this region of p53 mRNA to bind protein factors was also described with special emphasis on general principles that govern, such RNA-protein interactions. The structural alterations within the 5′-terminal region of p53 mRNA and proteins that bind to this region have a strong impact on the rate of mRNA scanning and on translation efficiency in in vitro assays, in selected cell lines, and under stress conditions. Thus, the structural features of the 5′-terminal region of p53 mRNA seem to be very important for translation and for translation regulation mechanisms. Finally, we suggested topics that, in our opinion, should be further explored for better understanding of the mechanisms of the p53 gene expression regulation at the translational level.

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