Inhibiting S100B Restores p53 Levels in Primary Malignant Melanoma Cancer Cells

Abstract

S100 calcium-binding proteins such as S100B are elevated in primary malignant melanoma and are used as markers for this and numerous other cancers. Wild-type p53 protein levels are relatively low in these cancer cells (i.e. when compared with cells without S100B) but are elevated when RNA antisense to S100B is introduced. This result implicates S100B in the down-regulation of p53 and is consistent with the large decreases in p53 protein levels observed previously in transient cotransfections of p53 and S100B (Lin, J., Blake, M., Tang Down-regulation of p53 in primary malignant melanoma cells is likely the result of a direct interaction with S100B, which was observed by co-immunoprecipitation experiments. Furthermore, p53 binds regions of the S100B promoter, one of which matches the 20-nucleotide p53-binding consensus DNA sequence perfectly. Therefore, when p53 levels increase, it contributes to its own demise by up-regulating the transcription of S100B as part of a negative feedback loop. This is analogous to what is found for another protein that down-regulates p53, namely hdm2 (human double mutant 2).

The Calcium-binding Protein S100B Down-regulates p53 and Apoptosis in Malignant Melanoma

“…1). The p53 status in both the C8146A and SK-MEL-28 cell lines was confirmed (26,39), and both the SK-MEL-28 and the C8146A cells were found to encode p53 with an arginine residue at position 72, which is the more abundant residue at this polymorphic site. Melanoma cells were grown in RPMI 1640 media (Invitrogen) containing 10% fetal bovine serum in the absence of antibiotics.…”

“…With the LOX-MM as an exception, which has low levels of S100B and wild-type p53, the other melanoma cells all have elevated levels of S100B and wild type of p53 (26,34). Malignant melanoma cells (SK-MEL-28), which have similarly elevated S100B levels and mutated p53 (p53R145L), were purchased from the American Type Culture Collection (Fig.…”

“…Melanoma cells were grown in RPMI 1640 media (Invitrogen) containing 10% fetal bovine serum in the absence of antibiotics. siRNA-As previously described (26), three siRNA constructs (termed siRNA S100B ) reduced S100B mRNA by 5-to 7-fold as determined by qPCR. However, the highly stable S100B protein was only reduced by ϳ2-fold when dually transfected at 24 and 48 h, as previously reported (26).…”

“…S100B, a 21.5-kDa symmetric homodimer, is overexpressed in malignant melanoma (18), anaplastic astrocytomas (20), and glio-blastomas (21), and in the case of malignant melanoma, high concentrations of S100B correlate directly with poor prognosis in patients (22). More recently, S100B has gained attention, because it binds directly to the p53 tumor suppressor protein in melanoma (23)(24)(25)(26), reduces p53 protein levels (26,27), and inhibits wild-type p53 functions in malignant melanoma (26 -28). Such S100B-dependent effects on p53 are cell-specific, because there is also evidence that S100B rescued a temperature-sensitive p53val135 mutant in fibroblast cell lines (25,29,30).…”

S100B Increases Proliferation in PC12 Neuronal Cells and Reduces Their Responsiveness to Nerve Growth Factor via Akt Activation

“…However, we cannot exclude the possibility that S100B might use different mechanisms to regulate cell proliferation in different cell types. For example, inhibitory effects of (overexpressed) S100B on the tumor suppressor activity of p53 might be restricted to neoplastic cells, as suggested by recent data showing that in primary malignant melanoma cells, p53 induces S100B expression, which in turn down-regulates p53 expression (43).…”