Metabolic orchestration of cell death by AMPK-mediated phosphorylation of RIPK1

Adenosine monophosphate-activated protein kinase (AMPK) activity is stimulated to promote metabolic adaptation upon energy stress. However, sustained metabolic stress may cause cell death. The mechanisms by which AMPK dictates cell death are not fully understood. We report that metabolic stress promoted receptor-interacting protein kinase 1 (RIPK1) activation mediated by TRAIL receptors, whereas AMPK inhibited RIPK1 by phosphorylation at Ser415 to suppress energy stress-induced cell death. Inhibiting pS415-RIPK1 by Ampk deficiency or RIPK1 S415A mutation promoted RIPK1 activation. Furthermore, genetic inactivation of RIPK1 protected against ischemic injury in myeloid Ampkα1-deficient mice. Our studies reveal that AMPK phosphorylation of RIPK1 represents a crucial metabolic checkpoint, which dictates cell fate response to metabolic stress, and highlight a previously unappreciated role for the AMPK-RIPK1 axis in integrating metabolism, cell death, and inflammation.

Lactate Lights up PI3K Inhibitor Resistance in Breast Cancer

Predictive biomarkers can facilitate optimal patient selection for targeted cancer therapies. In this issue of Cancer Cell, Ros et al. show the utility of noninvasive metabolic imaging of labeled carbon transfer from pyruvate to lactate to detect early response and FOXM1-mediated resistance to PI3K inhibition in estrogen-receptor-positive breast cancer.

PKM2 is not required for pancreatic ductal adenocarcinoma

BACKGROUND

While most cancer cells preferentially express the M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2), PKM2 is dispensable for tumor development in several mouse cancer models. PKM2 is expressed in human pancreatic cancer, and there have been conflicting reports on the association of PKM2 expression and pancreatic cancer patient survival, but whether PKM2 is required for pancreatic cancer progression is unknown. To investigate the role of PKM2 in pancreatic cancer, we used a conditional allele to delete PKM2 in a mouse model of pancreatic ductal adenocarcinoma (PDAC).

RESULTS

PDAC tumors were initiated in LSL-Kras G12D/+ ;Trp53 flox/flox ;Pdx-1-Cre (KP-/-C) mice harboring a conditional Pkm2 allele. Immunohistochemical analysis showed PKM2 expression in wild-type tumors and loss of PKM2 expression in tumors from Pkm2 conditional mice. PKM2 deletion had no effect on overall survival or tumor size. Loss of PKM2 resulted in pyruvate kinase M1 (PKM1) expression, but did not affect the number of proliferating cells. These findings are consistent with results in other cancer models.

CONCLUSIONS

PKM2 is not required for initiation or growth of PDAC tumors arising in the KP-/-C pancreatic cancer model. These findings suggest that, in this mouse PDAC model, PKM2 expression is not required for pancreatic tumor formation or progression.

PKM2 is not required for colon cancer initiated by APC loss

BACKGROUND

Cancer cells express the M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2). PKM2 expression is not required for some cancers, and PKM2 loss can promote cancer progression; however, PKM2 has been reported to be essential in other tumor contexts, including a proposed non-metabolic role in β-catenin nuclear translocation. PKM2 is expressed in colon cancers where loss of the Apc tumor suppressor results in β-catenin nuclear translocation and aberrant activation of the canonical Wnt signaling pathway. Whether PKM2 is required in this colon cancer context has not been investigated.

RESULTS

Colon tumorigenesis was induced in mice harboring conditional Apc and Pkm2 alleles, and tumor progression was monitored by serial colonoscopy. PKM2 deletion had no effect on overall survival, the number of mice that developed tumors, or the number of tumors that developed per animal. Immunohistochemical analysis demonstrated PKM2 expression in wild-type tumors and the expected loss of PKM2 expression in tumors from Pkm2 conditional mice. Loss of PKM2 resulted in pyruvate kinase M1 expression but had no effect on nuclear β-catenin staining. These findings are consistent with tumor growth and activated Wnt signaling despite PKM2 loss in this model. We also found a large fraction of human colon cancers had very low or undetectable levels of PKM2 expression.

CONCLUSIONS

PKM2 is not required for Apc-deficient colon cancer or for nuclear translocation of β-catenin in Apc-null tumor cells. These findings suggest that PKM2 expression is not required for colon tumor formation or progression.