CD38 is a putative functional marker for side population cells in human nasopharyngeal carcinoma cell lines

Cancer stem cells (CSCs) are thought to be responsible for cancer progression and therapeutic resistance but identification of this subpopulation requires selective markers. Fortunately, side population (SP) cells analysis brings a novel method to CSCs study. In this study, we identified SP cells, which are demonstrated rich in CSCs, in four nasopharyngeal carcinoma (NPC) cell lines. We investigated SP cells from HK-1 NPC cell line and showed CSCs characteristics in this subpopulation. SP cells displayed greater proliferation and invasion and expressed high levels of CSCs markers than NSP cells. Furthermore, our microRNA microarray analysis of SP versus NSP cells revealed that CD38-related miRNAs were down-regulated in SP cell, but the mRNA and protein level of CD38 were highly expressed in SP cells. We further searched for molecules interacting with CD38 and identified ZAP70, which was also well expressed in SP cells at both mRNA and protein levels. Our results uncover a CD38 pathway that may regulate the proliferation and migration of SP cells from HK-1 NPC cell line.