Metabolic Stress-Induced Phosphorylation of KAP1 Ser473 Blocks Mitochondrial Fusion in Breast Cancer Cells

Abstract

Mitochondrial dynamics during nutrient starvation of cancer cells likely exert profound effects on their capability for metastatic progression. Here we report that KAP1 (TRIM28), a transcriptional co-adaptor protein implicated in metastatic progression in breast cancer, is a pivotal regulator of mitochondrial fusion in glucose-starved cancer cells. Diverse metabolic stresses induced Ser473-phosphorylation of KAP1 (pS473-KAP1) in a ROS- and p38-dependent manner. Results from live cell imaging and molecular studies revealed that during the first 6–8 hr of glucose starvation mitochondria initially underwent extensive fusion, but then subsequently fragmented in a pS473-KAP1-dependent manner. Mechanistic investigations using phosphorylation-defective mutants revealed that KAP1 Ser473-phosphorylation limited mitochondrial hyperfusion in glucose-starved breast cancer cells, as driven by downregulation of the mitofusin protein MFN2, leading to reduced oxidative phosphorylation and ROS production. In clinical specimens of breast cancer, reduced expression of MFN2 corresponded to poor prognosis in patients. In a mouse xenograft model of human breast cancer, there was an association in the core region of tumors between MFN2 downregulation and the presence of highly fragmented mitochondria. Collectively, our results suggest that KAP1 Ser473 phosphorylation acts through MFN2 reduction to restrict mitochondrial hyperfusion, thereby contributing to cancer cell survival under conditions of sustained metabolic stress.

Mitochondrial division inhibitor (mdivi-1) decreases oxidative metabolism in cancer

“…4,19 Mdivi-1 increased OCR in non-cancer cells like mouse neuroblastoma 58 but deceased OCR in human ductus arteriosus smooth muscle cells. 59 Similar to these findings, studies showed that mdivi-1 increased OCR in some cancer cells 60,61 but decreased OCR in other cancer cells. 25,62 To better understand the regulatory role of DRP1 in cancer metabolism, we used [U- 13 C] glucose tracing to directly reveal the intracellular glucose metabolism in DRP1-deficient H460 lung cancer cells and in multiple mdivi-1-treated cancer cell lines.…”

The lncRNA BORG Drives Breast Cancer Metastasis and Disease Recurrence

“…4c ), a molecule previously speculated to function as an RNA-binding protein 40 . More recent evidence suggests that TRIM28 plays an oncogenic role in numerous human malignancies 41 – 44 , including several studies linking TRIM28 to the metastatic progression of breast cancers 17 , 45 – 47 . Interestingly, the ability of TRIM28 to enhance the malignancy of breast cancer cells transpires in part through its transcriptional repression of both p21 and gadd45a 15 , 16 , 18 , two transcripts whose expression is negatively regulated by BORG in D2.OR cells (Fig.…”

KAP1 facilitates reinstatement of heterochromatin after DNA replication

“…KAP1 can be subjected to several post-translational modifications (PTM) including sumoylation, ubiquitination and phosphorylation. Among these, phosphorylation on serine 473 (S473) was observed in the setting of DNA damage ( 35 ), metabolic stress ( 36 ), T cell receptor activation ( 37 , 38 ) and KSHV (Kaposi's sarcoma-associated herpervirus ) infection ( 39 ), and to be mediated by PKCδ (Protein Kinase C δ) during S phase ( 40 ). We thus examined the influence of the cell cycle on this KAP1 PTM by performing IF with a pS473KAP1-specific antibody on NIH3T3 cells synchronized by 3 days of serum starvation followed by serum re-addition.…”