Abstract
PPM1D/Wip1 is a negative regulator of the tumor suppressor p53 and is overexpressed in several human solid tumors. Recent reports associate gain-of-function mutations of PPM1D in immune cells with worse outcomes for several human cancers. Here we show that mice with genetic knockout of Ppm1d or with conditional knockout of Ppm1d in the hematopoietic system, in myeloid cells, or in neutrophils all display significantly reduced growth of syngeneic melanoma or lung carcinoma tumors. Ppm1d knockout neutrophils infiltrate tumors extensively. Chemical inhibition of Wip1 in human or mouse neutrophils increases anti-tumor phenotypes, p53-dependent expression of co-stimulatory ligands, and proliferation of co-cultured cytotoxic T cells. These results suggest that inhibition of Wip1 in neutrophils enhances immune anti-tumor responses.
Highlights
PPM1D/Wip[1] is a negative regulator of the tumor suppressor p53 and is overexpressed in several human solid tumors
Through the Knock-Out Mouse Project (KOMP)[43], exon 3 of the Ppm1d gene was identified as a critical exon, deletion of which results in loss of Wip[1] expression and function (Supplementary Fig. 1a)
Through subsequent crosses of F2 progeny with C57Bl/6 β-actin-cre mice or C57Bl/6 β-actin-flp mice, respectively, we generated mice bearing the Ppm1dTm1b(KOMP)Wtsi allele, a germline Ppm1d knockout that expresses the LacZ reporter protein under the control of the endogenous Ppm1d promoter, or mice bearing the conditional knockout allele Ppm1dTm1c(KOMP)Wtsi, which expresses wild-type Wip[1]
Summary
PPM1D/Wip[1] is a negative regulator of the tumor suppressor p53 and is overexpressed in several human solid tumors. Chemical inhibition of Wip[1] in human or mouse neutrophils increases anti-tumor phenotypes, p53-dependent expression of co-stimulatory ligands, and proliferation of cocultured cytotoxic T cells. These results suggest that inhibition of Wip[1] in neutrophils enhances immune anti-tumor responses. The presence of protein-truncating variants (PTVs) of PPM1D in immune cells but not in tumors of breast and ovarian cancer patients was associated with worse outcomes[31]. These somatic PTVs of the PPM1D gene were clustered in exon 6 and conferred “gain-of-function” through increased protein stability and activity[32]. We initiated a study of the effects of Wip[1] expression levels or activity on antitumor immune responses
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