RGCC-mediated PLK1 activity drives breast cancer lung metastasis by phosphorylating AMPKα2 to activate oxidative phosphorylation and fatty acid oxidation

BACKGROUND

More than 90% of the mortality of triple-negative breast cancer (TNBC) patients is attributed to cancer metastasis with organotropism. The lung is a frequent site of TNBC metastasis. However, the precise molecular mechanism for lung-specific metastasis of TNBC is not well understood.

METHODS

RNA sequencing was performed to identify patterns of gene expression associated with lung metastatic behavior using 4T1-LM3, MBA-MB-231-LM3, and their parental cells (4T1-P, MBA-MB-231-P). Expressions of RGCC, called regulator of cell cycle or response gene to complement 32 protein, were detected in TNBC cells and tissues by qRT-PCR, western blotting, and immunohistochemistry. Kinase activity assay was performed to evaluate PLK1 kinase activity. The amount of phosphorylated AMP-activated protein kinase α2 (AMPKα2) was detected by immunoblotting. RGCC-mediated metabolism was determined by UHPLC system. Oxidative phosphorylation was evaluated by JC-1 staining and oxygen consumption rate (OCR) assay. Fatty acid oxidation assay was conducted to measure the status of RGCC-mediated fatty acid oxidation. NADPH and ROS levels were detected by well-established assays. The chemical sensitivity of cells was evaluated by CCK8 assay.

RESULTS

RGCC is aberrantly upregulated in pulmonary metastatic cells. High level of RGCC is significantly related with lung metastasis in comparison with other organ metastases. RGCC can effectively promote kinase activity of PLK1, and the activated PLK1 phosphorylates AMPKα2 to facilitate TNBC lung metastasis. Mechanistically, the RGCC/PLK1/AMPKα2 signal axis increases oxidative phosphorylation of mitochondria to generate more energy, and promotes fatty acid oxidation to produce abundant NADPH. These metabolic changes contribute to sustaining redox homeostasis and preventing excessive accumulation of potentially detrimental ROS in metastatic tumor cells, thereby supporting TNBC cell survival and colonization during metastases. Importantly, targeting RGCC in combination with paclitaxel/carboplatin effectively suppresses pulmonary TNBC lung metastasis in a mouse model.

CONCLUSIONS

RGCC overexpression is significantly associated with lung-specific metastasis of TNBC. RGCC activates AMPKα2 and downstream signaling through RGCC-driven PLK1 activity to facilitate TNBC lung metastasis. The study provides implications for RGCC-driven OXPHOS and fatty acid oxidation as important therapeutic targets for TNBC treatment.

RGCC balances self-renewal and neuronal differentiation of neural stem cells in the developing mammalian neocortex

During neocortical development, neural stem cells (NSCs) divide symmetrically to self-renew at the early stage and then divide asymmetrically to generate post-mitotic neurons. The molecular mechanisms regulating the balance between NSC self-renewal and neurogenesis are not fully understood. Using mouse in utero electroporation (IUE) technique and in vitro human NSC differentiation models including cerebral organoids (hCOs), we show here that regulator of cell cycle (RGCC) modulates NSC self-renewal and neuronal differentiation by affecting cell cycle regulation and spindle orientation. RGCC deficiency hampers normal cell cycle process and dysregulates the mitotic spindle, thus driving more cells to divide asymmetrically. These modulations diminish the NSC population and cause NSC pre-differentiation that eventually leads to brain developmental malformation in hCOs. We further show that RGCC might regulate NSC spindle orientation by affecting the organization of centrosome and microtubules. Our results demonstrate that RGCC is essential to maintain the NSC pool during cortical development and suggest that RGCC defects could have etiological roles in human brain malformations.