The PTPROt tyrosine phosphatase functions as an obligate haploinsufficient tumor suppressor in vivo in B-cell chronic lymphocytic leukemia

Abstract

The tyrosine phosphatase PTPROt is a suggested tumor suppressor (TS) in B-cell chronic lymphocytic leukemia (CLL), and its expression is reduced in this disease. In order to examine how reduced PTPROt expression affects CLL in vivo we induced CLL in PTPROt-targeted mice. Unexpectedly, loss of both Ptprot alleles delayed disease detection and progression and lengthened survival relative to mice carrying two intact alleles, indicating that PTPROt fulfills a novel tumor-promoting role in CLL. Tumor cells from mice lacking PTPROt exhibited reduced B-cell receptor (BCR)-induced signaling, as well as increased apoptosis and autophagy. Inhibition of BCR/Src signaling in CLL cells induced their apoptosis, indicating that these findings are linked causally. These results suggest a cell-autonomous mechanism for the weakened CLL phenotype of PTPROt-deficient mice and uncover non-redundant roles for PTPROt in support of BCR signaling and survival of CLL cells. In contrast, loss of only one Ptprot allele induced earlier detection and progression of CLL and reduced survival, consistent with a tumor-suppressing role for PTPROt. Tumor cells from mice lacking one or both Ptprot allele exhibited increased interleukin-10 (IL-10) expression and signaling, factors known to support CLL; cells lacking one Ptprot alleles exhibited normal BCR signaling and cell death rates. We conclude that loss of one Ptprot allele promotes CLL, most likely by activating IL-10 signaling. Loss of both Ptprot alleles also reduces BCR signaling and increases cell death rates, offsetting the IL-10 effects and reducing the severity of the disease. PTPROt thus functions as an obligate haploinsufficient TS in CLL, where its expression levels determine its role as a promoter or inhibitor of the tumorigenic process in mice. Partial loss of PTPROt generates the strongest disease phenotype, suggesting that its intermediate expression levels in CLL are selected for.

TCL1A, B Cell Regulation and Tolerance in Renal Transplantation

“…IL-10 expression was higher in the tumor cells from the HET/Eµ-TCL1A mice and even higher in the ROKO/Eµ-TCL1A mice than in WT/Eµ-TCL1A mice, suggesting that PTPROt decreases enhanced IL-10 expression. In tumor cells, higher expression of IL-10R1 was observed in HET and ROKO/Eµ-TCL1A mice, consistent with higher phosphorylation of STAT3 activated by the IL-10 receptor [157]. In addition, this finding needs to be specifically extended to understand how PTPROt expression may influence that of IL-10; it may also have a link to the higher IL-10 potency found in WT/TCL1A mice [113], which may be explained partially by TCL1A repression of PTPROt and acquisition of a B10 phenotype.…”

“…Deleted PTPROt did not alter BCR signaling pathways, as indicated by WT, HET and ROKO mice presenting similar basal levels of Lyn, Syk, p-Akt and p-ERK. In Eµ-TCL1A mice, PTPROt may be considered a tumor repressor when one allele is deleted and, unexpectedly, may be a tumor promoter when both alleles are deleted [157]. IL-10 expression was higher in the tumor cells from the HET/Eµ-TCL1A mice and even higher in the ROKO/Eµ-TCL1A mice than in WT/Eµ-TCL1A mice, suggesting that PTPROt decreases enhanced IL-10 expression.…”

Phosphorylation of the phosphatase PTPROt at Tyr 399 is a molecular switch that controls osteoclast activity and bone mass in vivo

“…To examine the possible role of PTPROt in vivo in OCLs, we examined mice in which the distal P2 promoter of the Ptpro gene, which drives PTPROt production (25), was disrupted [ROKO (PTPROt knockout) mice] (32). Both PTPROt mRNA expression and production of PTPROt protein are abrogated in these mice, whereas expression of Glepp-1, the other product of the Ptpro gene, and production of GLEPP-1 protein is not affected (32). PTPROt, but not GLEPP-1, was present in OCLs from wild-type mice, and neither isoform was present in osteoblasts [ Fig.…”

“…The asterisk marks likely PTPROt alternative splicing products. The antibody against PTPROt cross-reacts with GLEPP-1 (32), and the arrow marks the expected location of the GLEPP-1 band. Molecular size markers are indicated in kilobases.…”

“…The rabbit polyclonal antibody that recognizes both PTPROt and GLEPP-1 has been described (32). Also used were mouse monoclonal antibodies against phosphotyrosine (PY99, Santa Cruz Biotechnology and PY20, BD Transduction Laboratories); HA [clone HA-7, coupled to beads (immunoprecipitation), Sigma-Aldrich and clone HA.11 (blotting and PLA), BioLegend]; actin (clone AC-40, Sigma-Aldrich); tubulin (clone DMIA, Sigma-Aldrich); and FLAG (clone M2, Sigma-Aldrich).…”