The serine threonine kinase RIP3: lost and found

Abstract

Receptor-interacting protein kinase-3 (RIP3, or RIPK3) is an essential protein in the "programmed", or "regulated" necrosis cell death pathway that is activated in response to death receptor ligands and other types of cellular stress. Programmed necrotic cell death is distinguished from its apoptotic counterpart in that it is not characterized by the activation of caspases; unlike apoptosis, programmed necrosis results in plasma membrane rupture, thus spilling the contents of the cell and triggering the activation of the immune system and inflammation. Here we discuss findings, including our own recent data, which show that RIP3 protein expression is absent in many cancer cell lines. The recent data suggests that the lack of RIP3 expression in a majority of these deficient cell lines is due to methylation-dependent silencing, which limits the responses of these cells to pro-necrotic stimuli. Importantly, RIP3 expression may be restored in many cancer cells through the use of hypomethylating agents, such as decitabine. The potential implications of loss of RIP3 expression in cancer are explored, along with possible consequences for chemotherapeutic response.

Fig. 1.. Expression of RIP3 in cancer or other cell lines (solid tumors or comparable tissues). The table shows showing the RIP3 expression in various cancer (solid tumors) and other cell lines cell lines as determined by western blotting and or reverse transcription-PCR. The estimated relative expression range of the cell is indicted (- to +++, with +++ indicating maximal expression and − indicating no expression detected; tr indicates some very low trace expression). For some cell lines, where indicated, the table shows whether the treatment of the cell line with 5-AD or other hypomethylating agents leads to increased expression of RIP3 mRNA or protein. The following abbreviations for citations are used: F, Fukasawa et al. ; H, He et al. ; K, Koo et al. ; Ki, Kim et al. ; M, Motani et al. ; N, Nugues et al. ; Z, Zhang et al. .

Fig. 2.. Expression of RIP3 in cell lines derived from hematological malignancies and murine cell lines. The tables show showing the RIP3 expression in various cancer and other cell lines cell lines as determined by western blotting and or reverse transcription-PCR. Murine cell lines are shown in the right panel. The estimated relative expression range of the cell is indicted (- to +++, with +++ indicating maximal expression and − indicating no expression detected; tr indicates some very low trace expression). For some cell lines, where indicated, the table shows whether the treatment of the cell line with 5-AD or other hypomethylating agents leads to increased expression of RIP3 mRNA or protein. The following abbreviations for citations are used: H, He et al. ; K, Koo et al. ; M, Motani et al. ; N, Nugues et al. ; Z, Zhang et al. , ^*Y.-S. Kim, unpublished observation.

Fig. 3.. RIP3 is silenced by methylation in multiple cancer and other cell lines, but can be upregulated in response to hypomethylation agents, such as decitabine (5-AD). (A) Western blotting showing the RIP3 expression in various cancer cell lines in response to 5-AD (2 ㎛) for 4 d. (B) Reverse transcription-PCR products from cancer cell lines following 4 d treatment with 5-AD (2 ㎛). (C) Western blotting showing the lack of RIP3 expression in Murine Embryonic Fibroblast (MEF) cell lines, including RIP-/- MEFs characterized by Zhang et al. . (D) Western blotting showing the RIP3 expression in MEF cell lines in (B) in response to 5-AD (2 ㎛) for 4 d.