Transcriptional Basis of Ca2+ Remodeling Reversal Induced by Polyamine Synthesis Inhibition in Colorectal Cancer Cells

Abstract

Colorectal cancer (CRC) is associated with mutations in APC/Wnt leading to c-myc activation and the overexpression of ODC1, the limiting step in polyamine synthesis. CRC cells also display a remodeling of intracellular Ca²⁺ homeostasis that contributes to cancer hallmarks. As polyamines may modulate Ca²⁺ homeostasis during epithelial tissue repair, we investigated whether polyamine synthesis inhibition may reverse Ca²⁺ remodeling in CRC cells and, if so, the molecular basis for this reversal. To this end, we used calcium imaging and transcriptomic analysis in normal and CRC cells treated with DFMO, an ODC1 suicide inhibitor. We found that polyamine synthesis inhibition partially reversed changes in Ca²⁺ homeostasis associated with CRC, including a decrease in resting Ca²⁺ and SOCE along with an increased Ca²⁺ store content. We also found that polyamine synthesis inhibition reversed transcriptomic changes in CRC cells without affecting normal cells. Specifically, DFMO treatment enhanced the transcription of SOCE modulators CRACR2A; ORMDL3; and SEPTINS 6, 7, 8, 9, and 11, whereas it decreased SPCA2, involved in store-independent Orai1 activation. Therefore, DFMO treatment probably decreased store-independent Ca²⁺ entry and enhanced SOCE control. Conversely, DFMO treatment decreased the transcription of the TRP channels TRPC1 and 5, TRPV6, and TRPP1 while increasing TRPP2, thus probably decreasing Ca²⁺ entry through TRP channels. Finally, DFMO treatment enhanced the transcription of the PMCA4 Ca²⁺ pump and mitochondrial channels MCU and VDAC3 for enhanced Ca²⁺ extrusion through the plasma membrane and mitochondria. Collectively, these findings suggested the critical role of polyamines in Ca²⁺ remodeling in colorectal cancer.

Keywords: DFMO; TRP channels; colorectal cancer; intracellular calcium; mitochondria; polyamines; store-operated calcium entry; transcriptomic analysis.