MicroRNA-135a induced formation of CD133+ cell sub-population with cancer-initiating cell properties in cervical cancer

Abstract

Many tumors are known to possess a sub-population of the cells with stem cell-like properties such as self-renewal and differentiation. These cells are responsible for tumor recurrence and chemoresistance thus, reducing the effectiveness of treatments. MicroRNAs (miRNAs) are a group of small non-coding RNAs that inhibit protein expression through transcriptional or translational inhibition. MicroRNAs are aberrantly expressed in pathological conditions and microRNA-135a (miR-135a) is an oncogenic miRNA highly expressed in cervical squamous cell carcinoma. Force-expression of miR-135a in a HPV E6/E7-immortalized cervical epithelial cell line NC104-E6/E7 not only induced cervical cancer transformation but also induced the expression of CD133, a cancer stem cell marker in liver and brain cancer, in a small sub-population of the transformed cells. We found that the CD133+ cells possess significantly higher self-renewal ability in low cell-density non-adherent culture, higher expression of 2 chemoresistance-associated genes ATP-binding cassette sub-family B member 1 and ATP-binding cassette sub-family G member 2 by quantification real-time PCR, and higher expression of Oct4 and -catenin in functional and expression analyses when compared to the CD133- cells. Upon serum challenge, the CD133+ cells differentiated into keratinocyte with increased expression of involucrin and reduced expression of CD133, Oct4 and miR-135a. The CD133+ cells also had higher in-vivo tumorigenic potential compared to the CD133- cells, half of the immunosuppressive mice injected with as few as 500 of the CD133+ cells developed tumors while none of the mice developed tumor with injection of CD133- cells. In clinical biopsies, we did not observed expression of CD133 in normal cervical tissues but the expression was dramatically elevated in squamous cell carcinoma. The CD133+ cells isolated from primary cervical tumor also exhibited higher self-renewal ability than the CD133- counterpart. In summary, we demonstrated that miR-135a not only induced cancer transformation but also enhanced the formation of cells with cancer-stem cell properties. [The research is supported by a grant from Research Grant Council, Hong Kong].