Salivary protein histatin 3 regulates cell proliferation by enhancing p27(Kip1) and heat shock cognate protein 70 ubiquitination.

Histatins are salivary proteins with antimicrobial activities. We previously reported that histatin 3 binds to heat shock cognate protein 70 (HSC70), which is constitutively expressed, and induces DNA synthesis stimulation and promotes human gingival fibroblast (HGF) survival. However, the underlying mechanisms of histatin 3 remain largely unknown. Here, we found that the KRHH sequence of histatin 3 at the amino acid positions 5-8 was essential for enhancing p27(Kip1) (a cyclin-dependent kinase inhibitor) binding to HSC70 that occurred in a dose-dependent manner; histatin 3 enhanced the binding between p27(Kip1) and HSC70 during the G1/S transition of HGFs as opposed to histatin 3-M(5-8) (substitution of KRHH for EEDD in histatin 3). Histatin 3, but not histatin 3-M(5-8), stimulated DNA synthesis and promoted HGF survival. Histatin 3 dose-dependently enhanced both p27(Kip1) and HSC70 ubiquitination, whereas histatin 3-M(5-8) did not. These findings provide further evidence that histatin 3 may be involved in the regulation of cell proliferation, particularly during G1/S transition, via the ubiquitin-proteasome system of p27(Kip1) and HSC70.