Bacterial heat shock protein-60 increases epithelial cell proliferation through the ERK1/2 MAP kinases

Heat shock proteins (hsp) have important roles in the regulation and protec tion of both prokaryotic and eukaryotic cells, especially during environmen tal stress. Hsps are also important bacterial virulence factors. We investi gated whether bacterial hsp60 can alter epithelial cell mitogen-activated p rotein kinase (MAPK) signaling and cell proliferation. Human skin keratinoc ytes (HaCaT cell line) were cultured in the presence of hsp60 purified from Actinobacillus actinomycetemcomitans, an important oral pathogen. Protein kinases in the ERK1/2 and p38 MAPK signaling pathways were probed with kina se-specific and phosphorylation-site-specific antibodies on Western blots. In quiescent cultures, hsp60 increased ERK1/2 phosphorylation in a sustaine d manner and p38 phosphorylation transiently, Hsp60 also increased epitheli al cell proliferation by about 30%. Inhibition of the ERK1/2 pathway by PD 98059 (a MEK1 inhibitor) reversed partially ERK1/2 phosphorylation and tota lly cell proliferation indicating that the ERK1/2 MAPK pathway is involved in the hsp60-induced cell growth. This was supported by findings that hsp60 stimulated phosphorylation of RSK1/2 and cyclic AMP response element-bindi ng protein and increased expression of transcription factors c-Jun and c-Fo s. Recombinant human hsp60 did not alter ERK1/2 or p38 phosphorylation and had no effect on epithelial cell proliferation. Inhibition of p38 MAPK path way by SB 203580 increased both ERK1/2 phosphorylation and cell proliferati on demonstrating that the inhibitor can either directly or indirectly activ ate the ERK1/2 MAPK pathway. The results show that exogenous bacterial hsp6 0 is able to activate ERK1/2 phosphorylation and thereby cause increased ep ithelial proliferation. In case of mucosal infection this effect may either lead to increased wound repair or participate in the pathological mechanis m of some bacterial diseases that involve increased epithelial proliferatio n. (C) 2001 Academic Press.