title: L-3-Phosphoserine phosphatase (PSPH) regulates cutaneous squamous cell carcinoma proliferation independent of L-serine biosynthesis.
abstract: BACKGROUND
  L-3-Phosphoserine phosphatase (PSPH) is a highly conserved and widely expressed member of the haloacid dehalogenase superfamily and the rate-limiting enzyme in l-serine biosynthesis. We previously found Psph expression to be uniquely upregulated in a α6β4 integrin transgenic mouse model that is predisposed to epidermal hyperproliferation and squamous cell carcinoma (SCC) formation implicating a role for Psph in epidermal homeostasis.
  
  
  OBJECTIVE
  We examined the status of PSPH in normal skin epidermis and skin tumors along with its sub-cellular localization in epidermal keratinocytes and its requirement for squamous cell carcinoma (SCC) proliferation.
  
  
  METHODS
  First, an immunohistochemical study was performed for PSPH in normal skin and skin cancer specimens and in cultured keratinocytes. Next, biochemical analyses were performed to confirm localization of PSPH and to identify candidate binding proteins. Finally, proliferation and apoptosis studies were performed in human SCC and normal keratinocytes, respectively, transduced with vectors encoding small hairpin RNAs targeting PSPH or overexpressing a phosphatase-deficient PSPH mutant.
  
  
  RESULTS
  PSPH is expressed throughout the proliferative layer of the epidermis and hair follicles in rodent and human skin and is highly induced in SCC. In keratinocytes, PSPH is a cytoplasmic protein that primarily localizes to endosomes and is present primarily as a homodimer. Knock down of PSPH dramatically diminished SCC cell proliferation and cyclin D1 levels in the presence of exogenous of l-serine production suggesting a non-canonical role for PSPH in epithelial carcinogenesis.
  
  
  CONCLUSIONS
  Psph is highly induced in proliferative normal keratinocytes and in skin tumors. PSPH appears to be critical for the proliferation of SCC cells; however, this phenomenon may not involve the phosphoserine metabolic pathway.
authors: Department of Dermatology, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA.
authors: Michael A
authors: MA
authors: Bachelor
authors: Yan
authors: Y
authors: Lu
authors: David M
authors: DM
authors: Owens
mesh_terms: D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D002294:Carcinoma, Squamous Cell / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D049109:Cell Proliferation; D017931:DNA Primers / Q000235:genetics; D019281:Dimerization; D011992:Endosomes / Q000201:enzymology; D005260:Female; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000201:enzymology; D008297:Male; D051379:Mice; D009154:Mutation; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012694:Serine / Q000096:biosynthesis; D012878:Skin Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology
chemical_list: D017931:DNA Primers; D012694:Serine; D010744:Phosphoric Monoester Hydrolases; C022394:phosphoserine phosphatase