Heat shock protein 20 suppresses breast carcinogenesis by inhibiting the MAPK and AKT signaling pathways

Heat shock protein (HSP) 20 belongs to the small HSP family and exhibits diverse functions, including tumor suppression, in addition to being a molecular chaperon, which is the classical property of HSPs. The present study aimed to examine the association between HSP20 expression and breast cancer (BC) progression in patients, and to explore the possible role of HSP20 in malignant phenotypes of BC cells. A series of experiments, including reverse transcription-quantitative PCR, western blotting, Cell Counting Kit-8 and flow cytometry, were performed. Data from Gene Expression Omnibus and Kaplan-Meier Plotter revealed that HSP20 expression was significantly downregulated in BC tissues, and patients with BC with lower HSP20 expression exhibited poorer recurrence-free survival. The data revealed that HSP20 was closely associated with the pathological tumor stage (P=0.015) and pathological tumor node metastasis (P=0.031) of patients with BC. Additionally, HSP20 expression was markedly decreased in BC cell lines. Exogenous overexpression of HSP20 inhibited proliferation and accelerated apoptosis of BC cells. These cells exhibited decreased migration and invasion when HSP20 was overexpressed. Furthermore, HSP20 overexpression suppressed the MAPK and AKT signaling pathways, as evidenced by the reduced phosphorylation levels of AKT, ERK, JNK and p38. Knockdown of HSP20 exerted the opposite effects. Notably, the AKT agonist, SC79, and the ERK agonist, LM22B-10, reversed the decrease in cell proliferation and migration induced by HSP20 overexpression. Overall, the data suggest that the decreased expression of HSP20 in BC tissues may be associated with disease progression. HSP20 also attenuated the malignant phenotype of BC cells and the inhibition of MAPK and AKT signaling may be associated with this effect. Therefore, HSP20 may be a potential prognostic marker or a candidate therapeutic target for BC.