Dephosphorylation of cancer protein by tyrosine phosphatases in response to analogs of luteinizing hormone-releasing hormone and somatostatin

Lung Ta Lee, Andrew V Schally, Charles Liebow, Ping Ping Lee, Po Huang Lee, Ming Ting Lee

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Protein phosphorylation/dephosphorylation of tyrosine residues is an important regulatory mechanism in cell growth and differentiation. Previously it has been reported that RC-160, an octapeptide analog of somatostatin, and [D-Trp6]LHRH, an agonist of luteinizing hormone-releasing hormone (LHRH), stimulate receptor-mediated activity of tyrosine phosphatases (PTP) and reverse growth promotion of the tyrosine kinase (PTK) class of oncogenes in tumor cells. The effect of RC-160 and [D-Trp6]LHRH on protein phosphorylation was further examined in surgical specimens of human carcinomas. Protein extracts of human ovarian, liver, breast and prostate tumor samples were preincubated with epidermal growth factor (EGF) (10-7 M) with or without [D-Trp6]LHRH or RC-160 (10-6 M) at 25°C for 2 h, followed by incubation for 10 min with [γ-32p]ATP. SDS-PAGE, Western blotting, autoradiography and densitometry were then used to quantify the phosphorylation level of individual protein bands. It was found that EGF enhanced, and [D-Trp6]LHRH and RC-160 reduced phosphorylation of a prominent 300-kDa band. Two proteins (65 and 60 kDa), involved in growth control in tumor cell lines, were also identified in this study. The homology of substrate phosphorylation between induced PTK and PTP in the presence of hormones provided evidence that these substrates might be identical or related in tumors. These findings, along with the previous cell culture results, suggest that many solid tumors may respond to treatment with analogues of somatostatin and LHRH. Collectively, the results further support the hypothesis that these 60-, 65- and 300-kDa protein substrates may be involved in growth-message transduction.

Original languageEnglish
Pages (from-to)2599-2605
Number of pages7
JournalAnticancer Research
Volume28
Issue number5 A
StatePublished - Sep 1 2008

Fingerprint

Protein Tyrosine Phosphatases
Somatostatin
Gonadotropin-Releasing Hormone
Phosphorylation
Neoplasms
Proteins
Growth
Epidermal Growth Factor
Protein-Tyrosine Kinases
Tyrosine
LHRH Receptors
Densitometry
Tumor Cell Line
Autoradiography
Oncogenes
Phosphoric Monoester Hydrolases
Prostate
Polyacrylamide Gel Electrophoresis
Cell Differentiation
Cell Culture Techniques

Keywords

  • LHRH
  • Protein tyrosine kinase
  • Protein tyrosine phosphatase
  • Receptor
  • Somatostatin

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

Cite this

Dephosphorylation of cancer protein by tyrosine phosphatases in response to analogs of luteinizing hormone-releasing hormone and somatostatin. / Lee, Lung Ta; Schally, Andrew V; Liebow, Charles; Lee, Ping Ping; Lee, Po Huang; Lee, Ming Ting.

In: Anticancer Research, Vol. 28, No. 5 A, 01.09.2008, p. 2599-2605.

Research output: Contribution to journalArticle

Lee, Lung Ta ; Schally, Andrew V ; Liebow, Charles ; Lee, Ping Ping ; Lee, Po Huang ; Lee, Ming Ting. / Dephosphorylation of cancer protein by tyrosine phosphatases in response to analogs of luteinizing hormone-releasing hormone and somatostatin. In: Anticancer Research. 2008 ; Vol. 28, No. 5 A. pp. 2599-2605.
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