A basic peptide derived from the HARP C-terminus inhibits anchorage-independent growth of DU145 prostate cancer cells

Heparin affin regulatory peptide (HARP) is an 18 kDa heparin-binding protein that plays a key role in tumor growth. We showed previously that the synthetic peptide P(111–136) composed of the last 26 HARP amino acids inhibited HARP-induced mitogenesis. Here, to identify the exact molecular domain involved in HARP inhibition, we investigated the effect of the shorter basic peptide P(122–131) on DU145 cells, which express HARP and its receptor protein tyrosine phosphatase β/ζ (RPTPβ/ζ). P(122–131) was not cytotoxic; it dose-dependently inhibited anchorage-independent growth of DU145 cells. Binding studies using biotinylated P(122–131) indicated that this peptide interfered with HARP binding to DU145 cells. Investigation of the mechanisms involved suggested interference, under anchorage-independent conditions, of P(122–131) with a HARP autocrine loop in an RPTPβ/ζ-dependent fashion. Thus, P(122–131) may hold potential for the treatment of disorders involving RPTPβ/ζ.