title: Leptin induces upregulation of sphingosine kinase 1 in oestrogen receptor-negative breast cancer via Src family kinase-mediated, janus kinase 2-independent pathway.
abstract: BACKGROUND
  Obesity is a known risk factor for breast cancer. Sphingosine kinase 1 (SK1) is an oncogenic lipid kinase that is overexpressed in breast tumours and linked with poor prognosis, however, its role in obesity-driven breast cancer was never elucidated.
  
  
  METHODS
  Human primary and secondary breast cancer tissues were analysed for SK1 and leptin receptor expression using quantitative real-time polymerase chain reaction (qRT-PCR) assay. Leptin-induced signalling was analysed in human oestrogen receptor (ER)-positive and negative breast cancer cells using Western blotting, qRT-PCR and radiolabelling assays.
  
  
  RESULTS
  Our findings show for the first time that human primary breast tumours and associated lymph node metastases exhibit a strong correlation between SK1 and leptin receptor expression (Pearson R = 0.78 and R = 0.77, respectively, P <0.001). Both these genes are elevated in metastases of ER-negative patients and show a significant increase in patients with higher body mass index (BMI). Leptin induces SK1 expression and activation in ER-negative breast cancer cell lines MDAMB-231 and BT-549, but not in ER-positive cell lines. Pharmacological inhibition and gene knockdown showed that leptin-induced SK1 activity and expression are mediated by activation of extracellular signal-regulated kinases 1/2 (ERK1/2) and Src family kinase (SFK) pathways, but not by the major pathways downstream of leptin receptor (LEPR) - janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3). Src-homology 2 domain-containing phosphatase 2 (SHP2) appeared to be key to SK1 activation, and may function as an adaptor protein between SFKs and LEPR. Importantly, leptin-induced breast cancer cell proliferation was abrogated by SK1-specific small interfering RNA (siRNA).
  
  
  CONCLUSIONS
  Overall, our findings demonstrate a novel SFK/ERK1/2-mediated pathway that links leptin signalling and expression of oncogenic enzyme SK1 in breast tumours and suggest the potential significance of this pathway in ER-negative breast cancer.
authors.forename: Heba
authors.initials: H
authors.lastname: Alshaker
authors.forename: Jonathan
authors.initials: J
authors.lastname: Krell
authors.forename: Adam E
authors.initials: AE
authors.lastname: Frampton
authors.forename: Jonathan
authors.initials: J
authors.lastname: Waxman
authors.forename: Oleg
authors.initials: O
authors.lastname: Blyuss
authors.forename: Alexey
authors.initials: A
authors.lastname: Zaikin
authors.forename: Mathias
authors.initials: M
authors.lastname: Winkler
authors.forename: Justin
authors.initials: J
authors.lastname: Stebbing
authors.forename: Ernesto
authors.initials: E
authors.lastname: Yagüe
authors.forename: Dmitri
authors.initials: D
authors.lastname: Pchejetski
mesh_terms: D001943:Breast Neoplasms / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D049109:Cell Proliferation; D004790:Enzyme Induction; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism*; D020738:Leptin / Q000502:physiology*; D008207:Lymphatic Metastasis; D061986:MCF-7 Cells; D009765:Obesity / Q000150:complications / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11 / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism*; D054411:Receptors, Leptin / Q000378:metabolism; D015398:Signal Transduction; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D019061:src-Family Kinases; D000099157:Sphingosine Kinase
chemical_list: D053614:Janus Kinase 2; D020738:Leptin; D017853:Phosphotransferases (Alcohol Group Acceptor); D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D011960:Receptors, Estrogen; D054411:Receptors, Leptin; D042461:Vascular Endothelial Growth Factor A; D019061:src-Family Kinases; D000099157:Sphingosine Kinase; C515448:LEPR protein, human; C467484:VEGFA protein, human; C507924:JAK2 protein, human