Fluorescence Assisted Investigation of ERK1/2 Signaling in the Regulation of ATG3 and ATG5 Under Glutamine and Glucose Deprivation in Breast Cancer Cells

Extracellular signal-regulated kinases (ERKs) belong to the family of mitogen-activated protein kinases and transmit extracellular signals. The present study investigates ERK-mediated control of ATG3 and ATG5 as an adaptive response to glutamine and glucose deprivation, with the ERK-CREB axis implicated in this regulatory mechanism. Hyperactivation of ERKs plays a major role in tumor progression and differentiation. Phosphorylation of ERK1/2 at Thr202/Tyr204 residues was higher during glutamine and glucose starvation. Inhibition of ERK1/2 reduced cell viability, increased the presence of acidic vesicular organelle as observed by acridine orange fluorescence staining, and enhanced the expression levels of ATG3 and ATG5 proteins, signifying the protective role of ERK1/2 through control of ATG3 and ATG5 during starvation. The transcription factor CREB is activated by various kinases, including ERKs. Phosphorylation at Serine133 enables CREB to carry out transcriptional activation. Inhibition of ERK1/2 decreased CREB expression, suggesting that ERK1/2-dependent activation of CREB contributes to a reduction in cell viability and upregulation of ATG3 and ATG5 during glutamine and glucose starvation. Our findings collectively suggest that the ERK-mediated control of ATG3 and ATG5, in association with CREB, is essential for maintaining cell viability, serving as a stress adaptive strategy during glutamine and glucose starvation.