miR-135a induced formation of cancer-initialing cell subpopulation in cervical cancer

Abstract

Solid cancer is heterogeneous and some of the cells possess stem cell like properties, these cells are responsible for tumor growth, chemoresistance and tumor recurrence. MicroRNA (miRNA) is a small non-coding RNA that inhibits protein expression through transcription inhibition or translation repression. MicroRNA-135a (miR-135a) is a cervical cancer oncogenic miRNA and is highly expressed in squamous cell carcinoma. MiR-135a force-expression transformed the HPV-immortalized cervical epithelial cell line NC-104E6/E7 to cancer cells. A subpopulation of the transformed cells expressed CD133, which is a marker of cancer stem cells in liver and brain. We speculated that the miR-135a transformed CD133+ cells possess cancer-initialing cell properties. To examine the self-renewal ability, low cell-density non-adherent tumorsphere formation assay was performed. We found that the CD133+ cells had significantly higher tumorsphere forming ability when compared with the CD133- counterpart. The primary tumorspheres were collected and dissociated into single cells for secondary tumorspheres formation assay. The secondary tumorspheres took less time to develop and were larger than the primary tumorspheres. The CD133+ cells displayed significant higher expression of various chemoresistance-associated genes like ATP-binding cassette sub-family B member 1 and ATP-binding cassette sub-family G member 2. Besides, the pluripotent genes Oct4 and -catenin were also over-expressed in the CD133+ subpopulation. Upon serum challenges, the expression of CD133, Oct4 and miR-135a were decreased significantly while that of keratinocyte differentiation marker involucrin was increased. Taken together, we found that a subpopulation of miR-135a transformed HPV-E6/E7 immortalized cells possess in-vitro cancer-initialing cell properties. [The research is supported by a grant from Research Grant Council, Hong Kong].