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Regulation of antigen processing machinery component expression in head and neck cancer by signal transducers and activators of transcription and src homology-2 domain-containing phosphatase

Leibowitz, Michael Shinichi (2010) Regulation of antigen processing machinery component expression in head and neck cancer by signal transducers and activators of transcription and src homology-2 domain-containing phosphatase. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Squamous cell carcinoma of the head and neck (SCCHN) cells can escape recognition and lysis by tumor antigen (TA)-specific cytotoxic T lymphocytes (CTL) by downregulation of antigen processing machinery (APM) components, such as the transporter associated with antigen processing (TAP)-1/2 heterodimer. APM component upregulation by interferon gamma (IFN-g) restores SCCHN cell susceptibility to lysis by CTL, but the mechanism underlying TAP1/2 downregulation in SCCHN cells is not known. Because IFN-g activates signal transducer and activator of transcription (STAT)-1, we investigated phosphorylated (p)-STAT1 as a mediator of low basal TAP1/2 expression in SCCHN cells. SCCHN cells were found to express basal total STAT1 but low to undetectable levels of pSTAT1. The association of increased pSTAT1 levels and APM components likely reflects a cause-effect relationship, since STAT1 knockdown significantly reduced both IFN-g-mediated APM component expression and TA-specific CTL recognition of IFN-g treated SCCHN cells. On the other hand, since oncogenic pSTAT3 is overexpressed in SCCHN cells and was found to heterodimerize with pSTAT1, we also tested whether pSTAT3 and STAT1:STAT3 heterodimers inhibited IFN-g-induced APM component expression. First, STAT3 activation or depletion did not affect basal or IFN-g induced expression of pSTAT1 and APM components, or recognition of SCCHN cells by TA-specific CTL. Second, STAT1:STAT3 heterodimers did not interfere with IFN-g induced STAT1 binding to the TAP1 promoter or APM component protein expression. These findings demonstrate that APM component downregulation is regulated primarily by an IFN-g-pSTAT1-mediated signaling pathway, independent of STAT3 in SCCHN cells. Interestingly, treatment of SCCHN cells with a broad phosphatase inhibitor, sodium orthovanadate, increased pSTAT1 levels, suggesting that a phosphatase might be responsible for maintaining low basal pSTAT1 and APM component levels, as a mechanism for CTL escape by tumor cells. Indeed, immunohistochemical analyses of 14 SCCHN tumors and paired adjacent normal mucosa demonstrated that src homology-2 domain-containing phosphatase (SHP2) was significantly upregulated in the tumor tissue compared to surrounding mucosa. Moreover, SHP2 specific knockdown using siRNA resulted in significant upregulation of pSTAT1, APM components, and HLA class I in SCCHN cells. Furthermore, SHP2 depletion restored the recognition of SCCHN cells by TA-specific CTL, and induced secretion of Regulation upon Activation, Normal T cell Expressed, and presumably Secreted (RANTES) and IFN-g-inducible protein 10 (IP10). These novel findings identify SHP2 as an important molecular regulator contributing to low basal pSTAT1 levels and APM-mediated immune escape in SCCHN cells, and provide a potential inhibitory strategy for enhancing the clinical activity of T cell-based immunotherapy.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Leibowitz, Michael Shinichimsl7@pitt.eduMSL7
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairStorkus, Walter Jstorkuswj@upmc.eduSTORKUSW
Committee MemberRay, Anuradharaya@pitt.eduRAYA
Committee MemberGrandis,
Committee MemberBinder, Robertrjb42@pitt.eduRJB42
Committee MemberFerris, Robert Lferrisrl@upmc.eduRLF1
Date: 29 November 2010
Date Type: Completion
Defense Date: 18 November 2010
Approval Date: 29 November 2010
Submission Date: 24 November 2010
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Institution: University of Pittsburgh
Schools and Programs: School of Medicine > Immunology
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: antigen processing machinery; CTL; immune escape; STAT1; STAT3; SHP2
Other ID:, etd-11242010-131242
Date Deposited: 10 Nov 2011 20:06
Last Modified: 19 Dec 2016 14:37


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