Panoply™ Human CDK9 Knockdown Stable Cell Line

Aberrant activation of cyclin-dependent kinase 9 (CDK9) is widespread in human cancers. However, the underlying mechanisms of CDK9 activation and the potential of CDK9 inhibition in cervical cancer treatment remain largely unknown. Here, researchers found that CDK9 is progressively upregulated during cervical lesion progression and is regulated by the HPV16 E6 protein. CDK9 levels were highly correlated with FIGO stage, pathological grade, deep stromal invasion, tumor size, and lymph node metastasis. Specific siRNA knockdown of CDK9 inhibited cervical cancer cell proliferation in vitro and tumor formation in vivo. CDK9 inhibition led to a significant decrease in AKT2 protein expression and a significant increase in p53 protein expression, revealing a novel CDK9 regulatory mechanism. Overexpression of AKT2 reversed the inhibitory effects caused by CDK9 knockdown, indicating that AKT2 induction is crucial for CDK9-induced cell transformation. Furthermore, in HPV16-infected cervical cancer tissues, CDK9 expression was positively correlated with AKT2 and negatively correlated with p53. These studies demonstrate for the first time that CDK9 acts as an oncogene in cervical cancer, regulating cell proliferation and apoptosis through the AKT2/p53 pathway.

Here, researchers evaluated whether CDK9 gene knockdown could regulate the growth of cervical tumors in vivo. They subcutaneously transplanted CDK9-knockdown SiHa cells, SiHa control cells, CDK9-knockdown CaSki cells, and CaSki control cells into non-SCID mice. As shown in Figure 1A, the growth rate of CDK9-knockdown SiHa cells was significantly slower than that of control cells. Furthermore, the tumor volume formed by CDK9-knockdown SiHa cells was also significantly smaller than that formed by control cells (Figure 1B). Similarly, knockdown of the CDK9 gene in CaSki cells also resulted in a similar reduction in growth rate and tumor volume (Figure 1C, D). To further assess whether the regulatory effect of CDK9 on cell proliferation and apoptosis could be reproduced in vivo, researchers detected the expression of Ki-67 antigen (a known cell proliferation marker) by immunohistochemistry (IHC) and performed TUNEL assays. The number of Ki-67 antigen-positive cells in tumors formed by CDK9-knockdown cells was lower than that in tumors formed by control cells (Figure 1E, F). Consistent with the in vitro experimental data described above, TUNEL assay results showed that the apoptosis rate of CDK9-knockdown cells was significantly increased (Figure 1G, H). This further indicates that knocking down CDK9 expression can inhibit the growth of cervical cancer cells and induce apoptosis.

Figure 1. Knockdown of CDK9 expression suppresses subcutaneous tumor growth in non-SCID mice. (Xu J, et al., 2019)