Panoply™ Human CDK7 Over-expressing Stable Cell Line

Osteosarcoma originates from primitive osteogenic mesenchymal cells and is the most common primary malignant bone tumor. Currently, the treatment of osteosarcoma is not ideal; therefore, exploring new mechanisms of osteosarcoma pathogenesis is expected to provide new treatment options. CDK7 is a subunit of the general transcription factor TFIIH. Here, researchers aimed to explore novel mechanisms by which CDK7 regulates osteosarcoma and to provide new theoretical support for the application of CDK7 inhibitors in osteosarcoma treatment. They investigated the molecular mechanisms of interaction between CDK7 and GRP78 in osteosarcoma. Specifically, the researchers found that the E3 ubiquitin ligase TRIM21 binds to and targets GRP78 for ubiquitination and degradation, while CDK7 inhibits the recruitment of TRIM21 by phosphorylating the T69 site of GRP78, thereby stabilizing GRP78. Notably, the CDK7-specific inhibitor THZ1 can inhibit the growth and metastasis of osteosarcoma. Combined treatment with CDK7 and GRP78 inhibitors has a synergistic inhibitory effect on osteosarcoma growth and progression. Therefore, simultaneously inhibiting the activity of both CDK7 and GRP78 may represent a potential new approach for treating osteosarcoma.

To further elucidate the mechanism by which CDK7 promotes tumorigenesis, researchers attempted to identify interacting functional partners involved in CDK7-induced osteosarcoma growth and progression. Through immunoprecipitation and mass spectrometry analysis, GRP78 was identified as a potential candidate protein (Figure 1A, B). GRP78 is associated with increased malignancy and resistance to chemotherapy and radiotherapy in various cancers. Exogenous immunoprecipitation experiments in CDK7-overexpressing HEK-293T cells or GRP78-overexpressing HEK-293T cells confirmed this interaction (Figure 1C, D). Endogenous co-immunoprecipitation experiments in 143B cells also confirmed this interaction. To further support the intracellular interaction between CDK7 and GRP78, researchers performed cell fractionation and co-immunoprecipitation analysis, which showed that CDK7 could co-immunoprecipitate with GRP78 in both the nucleus and cytoplasm, and subsequent immunostaining confirmed this result (Figure 1E, F). CDK7 is a protein kinase reportedly involved in post-translational modification. Using recombinant human CDK7/Cyclin H/MNAT1 protein and His-tagged GRP78, researchers performed in vitro kinase activity assays and observed that GRP78 was phosphorylated by CDK7 (Figure 1G). Furthermore, in 143B cells, they also detected phosphorylated GRP78 using an anti-phosphothreonine-proline antibody (Figure 1H).

Figure 1. CDK7 interacts with GRP78. (Zhang T, et al., 2022)