The cellular stress sensor HSPB1 regulates the membrane localization of amino acid transporter SLC7A5 in breast cancer.

The heat shock protein beta-1 (HSPB1/HSP27) is highly expressed and phosphorylated in cancer tissues. However, the precise role of HSPB1 in cancer remains unclear. In this study, we report the unexpected findings elucidating the essential role of HSPB1 in adapting amino acid deficiency by upregulating amino acid transporter SLC7A5 function. HSPB1 regulates estrogen receptor-positive (ER+) breast cancer cell proliferation in a SLC7A5-dependent manner. In response to cellular stress, which is specified as amino acid-deficient conditions, HSPB1 was phosphorylated at Ser 78 residue by stress MAPK p38. SLC7A5 is associated with phosphorylated HSPB1 for its functional activation, leading to upregulated amino acid incorporation. In addition, HSPB1 and SLC7A5 overexpression increased acetylated α-tubulin levels. SLC7A5 overexpression did not change acetyl-CoA level, but SLC7A5 knockdown decreased ATAT1 and induced HDAC6 upregulation. Furthermore, HSPB1 and SLC7A5 induced paclitaxel and tamoxifen resistance. Therefore, the HSPB1-SLC7A5 axis contributes to the acquisition of tolerance to both tamoxifen and paclitaxel in breast cancer cells, uncovering a novel therapeutic target against drug resistance in breast cancer.