PAK5-Mediated Suppression of β-Hydroxybutyrate Production Promotes Breast Cancer Metastasis and Can Be Overcome with Ketogenic Diet

The ketogenic diet (KD) is an emerging metabolic approach for enhancing the efficacy of cancer therapy, and the KD is characterized by increased production of ketone bodies, including β-hydroxybutyrate (β-HB). Clarifying the direct effects of β-HB on cancer cells is critical for optimizing the therapeutic potential of KD. In this study, we show that β-HB levels were markedly decreased in tumor tissues and serum from patients with breast cancer, particularly in metastatic patients. Additionally, β-HB supplementation demonstrated potent antitumor effects in breast cancer models in vitro and in vivo. P21-activated kinase 5 (PAK5) inhibited β-HB synthesis by interacting with 3-hydroxy-3-methylglutaryl CoA synthase 2 (HMGCS2), a key enzyme in ketone generation, and inducing phosphorylation at Ser138 and Ser311. PAK5-mediated HMGCS2 Ser138 phosphorylation recruited the E3 ubiquitin ligase BMI1, thereby facilitating HMGCS2 degradation, and phosphorylation at Ser311 reduced the enzymatic activity of HMGCS2 by inhibiting SIRT3-dependent deacetylation. Collectively, phosphorylation at these two sites coordinately suppressed the generation of intracellular β-HB. Elevated PAK5 in breast cancer stimulated lymph node metastasis, whereas the expression of HMGCS2, particularly its nonphosphorylatable mutants, inhibited PAK5-driven breast tumor growth and metastasis. Consistently, KD or β-HB treatment could reverse breast cancer progression induced by PAK5. Low HMGCS2 expression and β-HB synthesis were associated with lymph node metastasis and poor clinical outcomes in patients, and PAK5 protein levels positively correlated with HMGCS2 phosphorylation at Ser311 residue in breast cancer tissues. Together, these findings demonstrated that the PAK5-HMGCS2 pathway drives breast cancer metastasis and can be circumvented using a KD. SIGNIFICANCE: PAK5-mediated phosphorylation of HMGCS2 promotes breast cancer growth and metastasis by inhibiting β-hydroxybutyrate production, revealing the role of PAK5 in ketone metabolism and highlighting a potential therapeutic target for breast cancer metastasis.