Mutation of SPINOPHILIN (PPP1R9B) found in human tumors promotes the tumorigenic and stemness properties of cells

Theranostics. 2021 Jan 19;11(7):3452-3471. doi: 10.7150/thno.53572. eCollection 2021.


Rationale: SPINOPHILIN (SPN, PPP1R9B) is an important tumor suppressor involved in the progression and malignancy of different tumors depending on its association with protein phosphatase 1 (PP1) and the ability of the PP1-SPN holoenzyme to dephosphorylate retinoblastoma (pRB). Methods: We performed a mutational analysis of SPN in human tumors, focusing on the region of interaction with PP1 and pRB. We explored the effect of the SPN-A566V mutation in an immortalized non-tumorigenic cell line of epithelial breast tissue, MCF10A, and in two different p53-mutated breast cancer cells lines, T47D and MDA-MB-468. Results: We characterized an oncogenic mutation of SPN found in human tumor samples, SPN-A566V, that affects both the SPN-PP1 interaction and its phosphatase activity. The SPN-A566V mutation does not affect the interaction of the PP1-SPN holoenzyme with pocket proteins pRB, p107 and p130, but it affects its ability to dephosphorylate them during G0/G1 and G1, indicating that the PP1-SPN holoenzyme regulates cell cycle progression. SPN-A566V also promoted stemness, establishing a connection between the cell cycle and stem cell biology via pocket proteins and PP1-SPN regulation. However, only cells with both SPN-A566V and mutant p53 have increased tumorigenic and stemness properties. Conclusions: SPN-A566V, or other equivalent mutations, could be late events that promote tumor progression by increasing the CSC pool and, eventually, the malignant behavior of the tumor.

Keywords: PP1; SPINOPHILIN; cancer stem cell; pRB; pocket proteins; stem cell phenotype; tumorigenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Breast Neoplasms / genetics*
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Carcinogenesis / genetics*
  • Carcinogenesis / metabolism
  • Carcinogenesis / pathology
  • Cell Line, Transformed
  • Cell Line, Tumor
  • Female
  • G1 Phase Cell Cycle Checkpoints / genetics
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Mice
  • Mice, Nude
  • Microfilament Proteins / genetics*
  • Microfilament Proteins / metabolism
  • Mutation*
  • Neoplastic Stem Cells / metabolism*
  • Neoplastic Stem Cells / pathology
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / metabolism
  • Phosphorylation
  • Protein Phosphatase 1 / genetics*
  • Protein Phosphatase 1 / metabolism
  • Resting Phase, Cell Cycle / genetics
  • Retinoblastoma Protein / genetics
  • Retinoblastoma Protein / metabolism
  • Signal Transduction
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • Xenograft Model Antitumor Assays


  • Microfilament Proteins
  • Nerve Tissue Proteins
  • Retinoblastoma Protein
  • Tumor Suppressor Protein p53
  • neurabin
  • Protein Phosphatase 1