Induction by rapamycin and proliferation‑promoting activity of Hspb1 in a Tsc2‑deficient cell line

Tuberous sclerosis complex (TSC) is an intractable inherited disease caused by a germline mutation in either the TSC complex subunit 1 (TSC1) or TSC2 tumor suppressor genes. Recent progress in the treatment of TSC with rapamycin has provided benefits to patients with TSC. However, the complete elimination of tumors is difficult to achieve as regrowth often occurs after a drug is suspended; thus, more efficient medication and novel therapeutic targets are required. To overcome tumor remnants in the treatment of TSC, the present study investigated rapamycin-responsive signaling pathways in Tsc2-deficient tumor cells, focusing on heat shock protein-related pathways. The expression levels of heat shock protein family B (small) member 1 (Hspb1; also known as HSP25/27) were increased by rapamycin treatment. The phosphorylation of Hspb1 was also increased. The knockdown of Hspb1 suppressed cell proliferation in the absence of rapamycin, and the overexpression of Hspb1 enhanced cell proliferation both in the presence and absence of rapamycin. Pathways associated with Hspb1 may present target candidates for treatment of TSC.