Loss of the tumor suppressor spinophilin (PPP1R9B) increases the cancer stem cell population in breast tumors

Abstract

The spinophilin (Spn, PPP1R9B) gene is located at 17q21.33, a region frequently associated with microsatellite instability and loss of heterozygosity, especially in breast tumors. Spn is a regulatory subunit of phosphatase1a (PP1), which targets the catalytic subunit to distinct subcellular locations. Spn downregulation reduces PPP1CA activity against the retinoblastoma protein, pRb, thereby maintaining higher levels of phosphorylated pRb. This effect contributes to an increase in the tumorigenic properties of cells in certain contexts. Here, we explored the mechanism of how Spn downregulation contributes to the malignant phenotype and poor prognosis in breast tumors and found an increase in the stemness phenotype. Analysis of human breast tumors showed that Spn mRNA and protein are reduced or lost in 15% of carcinomas, correlating with a worse prognosis, a more aggressive tumor phenotype and triple-negative tumors, whereas luminal tumors showed high Spn levels. Downregulation of Spn by shRNA increased the stemness properties along with the expression of stem-related genes (Sox2, KLF4, Nanog and OCT4), whereas ectopic overexpression of Spn cDNA reduced these properties. Breast tumor stem cells appeared to have low levels of Spn mRNA, and Spn loss correlated with increased stem-like cell appearance in breast tumors as indicated by an increase in CD44+/CD24- cells. A reduction of the levels of PPP1CA mimicked the cancer stem-like cell phenotype of Spn downregulation, suggesting that the mechanism of Spn involves PP1a. These increased cancer stem cell-like properties with reduced Spn might account for the malignant phenotype observed in Spn-loss tumors and may contribute to a worse patient prognosis.

Downregulation of MYPT1 increases tumor resistance in ovarian cancer by targeting the Hippo pathway and increasing the stemness

“…It was performed as previously described [31]. The shRNA PPP1R12A (MYPT1) and miRNA-30b were provided by Origene.…”

NAMPT Is a Potent Oncogene in Colon Cancer Progression that Modulates Cancer Stem Cell Properties and Resistance to Therapy through Sirt1 and PARP

“…It has been proposed that CICs are primarily responsible for tumor relapse and poor therapeutic responses, as CICs are able to reconstitute entire tumors. To analyze the cancer-initiating cell properties induced by NAMPT, we cultured cells at low densities to form independent colonies comprising individual clones, which were previously classified as holoclones, meroclones, and paraclones based on their ability to reconstitute tumors from a single cell (16)(17)(18)(19). Holoclones are believed to be derived from stem cells, whereas paraclones are differentiated cells that are incapable of reconstituting a culture ( Fig.…”

Coordinated downregulation of Spinophilin and the catalytic subunits of PP1, PPP1CA/B/C, contributes to a worse prognosis in lung cancer

“…Low levels of Spinophilin expression have been found in lung adenocarcinoma [ 7 ], head and neck cancer [ 8 ], hepatocellular carcinoma [ 9 ], human gastric, small intestine and colorectal adenocarcinoma [ 10 , 11 ], glioblastoma [ 12 ] and breast cancer [ 13 , 14 ]. In all cases, downregulation of Spinophilin correlated with a higher malignant grade, more aggressive biological behavior and resistance to therapies, leading to faster relapse and poorer patient survival.…”