Defective mitochondrial unfolded protein response in cancer acts as a lifeline for tumor growth and survival

Defective mitochondrial unfolded protein response (UPRmt) plays an important role in driving tumor growth and treatment resistance. Under physiological conditions, UPRmt preserves mitochondrial protein homeostasis and structure by inducing chaperones such as heat shock proteins (HSP60, HSP70, HSP10) and proteases like caseinolytic peptidase ATP-dependent, proteolytic subunit (ClpP), and Lon peptidase 1 (LONP1). However, dysfunctional UPRmt in cancer cells may allow them to tolerate mitochondrial damage and metabolic dysregulation and avoid cell death, thus promoting therapy resistance. Our current understanding of how transcriptional regulators such as activating transcription factor 5 (ATF5), C/EBP homologous protein (CHOP), and forkhead box protein O3a (FOXO3a), along with signaling circuits including ATF5-ATF4-CHOP, sirtuin 3 (SIRT3)-FOXO3a, and protein kinase B (AKT)-estrogen receptor alpha (ERα), coordinate detrimental forms of UPRmt activation in cancer cells remains limited. This review describes known interactions among mediators of the UPRmt pathway and how they may be dysregulated in cancer cells. We also explore how this altered stress response may provide avenues for therapeutic targeting.