SMAR1-derived P44 Peptide Retains Its Tumor Suppressor Function through Modulation of p53

Abstract

The use of pharmacologically active short peptide sequences is a better option in cancer therapeutics than the full-length protein. Here we report one such 44-mer peptide sequence of SMAR1 (TAT-SMAR1 wild type, P44) that retains the tumor suppressor activity of the full-length protein. The protein transduction domain of human immunodeficiency virus, type 1, Tat protein was used here to deliver the 33-mer peptide of SMAR1 into the cells. P44 peptide could efficiently activate p53 by mediating its phosphorylation at serine 15, resulting in the activation of p21 and in effect regulating cell cycle checkpoint. In vitro phosphorylation assays with point-mutated P44-derived peptides suggested that serine 347 of SMAR1 was indispensable for its activity and represented the substrate motif for the protein kinase C family of proteins. Using xenograft nude mice models, we further demonstrate that P44 was capable of inhibiting tumor growth by preventing cellular proliferation. P44 treatment to tumor-bearing mice prevented the formation of poorly organized tumor vasculature and an increase in hypoxia-inducible factor-1␣ expression, both being signatures of tumor progression. The chimeric TAT-SMAR1-derived peptide, P44, thus has a strong therapeutic potential as an anticancer drug.

SMAR1 Forms a Ternary Complex with p53-MDM2 and Negatively Regulates p53-mediated Transcription

“…For this purpose, we have used chemical shift perturbation experiments with a p53 peptide corresponding to residues 13-29 of p53, phosphorylated at Ser15 in the presence and in the absence of 44-mer SMAR1 peptide. 20 Results from Fig. 1c shows that the NH proton of Ser15 is clearly affected very significantly upon binding the SMAR1 peptide.…”

“…This was strengthened by our previous observations that SMAR1 specifically increased the phosphorylation of p53 at Ser15. 20 To identify the affinity of SMAR1 binding to p53, we used several N-terminal peptides of p53 that correspond to the serine-rich transactivation domain of p53. 22 These peptides were phosphorylated at specific serine/threonine residues; i.e.…”

“…17,18 Our recent studies demonstrate that a minimal domain of SMAR1 interacts with p53 and brings about its stabilization. 19,20 Moreover, SMAR1 is a stress-responsive protein and exists in a positive feedback loop with p53, stabilizing it after stress. 18 Here, we report that SMAR1 interacts both with p53 (phosphorylated at Ser15) and MDM2 independently.…”

Nuclear matrix-associated protein SMAR1 regulates alternative splicing via HDAC6-mediated deacetylation of Sam68

“…Loss of heterozygosity (LOH) in this locus is implicated in multiple cancers (7,8). SMAR1 delays tumor progression (9,10) and inhibits the expression of multiple genes (11,12). Clinical specimens of different histological grade breast cancer tissues indicated that SMAR1 expression is drastically down-regulated in the higher grades of infiltrating ductal carcinomas (13).…”

Tumor Suppressor SMAR1 Represses IκBα Expression and Inhibits p65 Transactivation through Matrix Attachment Regions

“…SMAR1 also inhibits tumor growth through p53 stabilization and cell cycle arrest (38). Further SMAR1-derived p44 peptide has been shown to actively inhibit tumor growth in vivo (39). Recently we have shown that SMAR1 is up-regulated upon doxorubicin treatment in a p53-dependent manner.…”