Oncotarget

Research Papers:

hPaf1/PD2 interacts with OCT3/4 to promote self-renewal of ovarian cancer stem cells

Saswati Karmakar, Parthasarathy Seshacharyulu, Imayavaramban Lakshmanan, Arokia P. Vaz, Seema Chugh, Yuri M. Sheinin, Sidharth Mahapatra, Surinder K. Batra and Moorthy P. Ponnusamy _

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Oncotarget. 2017; 8:14806-14820. https://doi.org/10.18632/oncotarget.14775

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Abstract

Saswati Karmakar1,*, Parthasarathy Seshacharyulu1,*, Imayavaramban Lakshmanan1, Arokia P. Vaz1, Seema Chugh1, Yuri M. Sheinin3, Sidharth Mahapatra4, Surinder K. Batra1,2, Moorthy P. Ponnusamy1,2

1Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, USA

2Fred and Pamela Buffett Cancer Center, Eppley Institute for Research in Cancer and Allied Disease, University of Nebraska Medical Center, Omaha, NE, USA

3Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE, USA

4Department of Pediatrics, University of Nebraska Medical Center, Omaha, NE, USA

*These authors contributed equally to this work

Correspondence to:

Moorthy P. Ponnusamy, email: [email protected]

Surinder K. Batra, email: [email protected]

Keywords: hPaf1/PD2, CSC, ovarian cancer, OCT3/4, self-renewal

Received: November 18, 2016     Accepted: January 11, 2017     Published: January 20, 2017

ABSTRACT

Cancer stem cells (CSCs), which mediate drug resistance and disease recurrence in several cancers, are therapeutically relevant to ovarian cancer (OC), wherein approximately 80% of patients manifest with tumor recurrence. While there are several markers for ovarian CSCs (OCSCs), the mechanism for their self-renewal maintenance by unique driver/markers is poorly understood. Here, we evaluated the role of hPaf1/PD2, a core component of RNA Polymerase II-Associated Factor (PAF) complex, in self-renewal of OCSCs through marker and functional analyses, including CRISPR/Cas9-silencing of hPaf1/PD2 in OCSCs and provided a possible mechanism for maintenance of OCSCs. Expression of hPaf1/PD2 showed moderate to intense staining in 32.4% of human OC tissues, whereas 67.6% demonstrated basal expression by immunohistochemistry analysis, implying that the minor proportion of cells overexpressing hPaf1/PD2 could be putative OCSCs. Isolated OCSCs showed higher expression of hPaf1/PD2 along with established CSC and self-renewal markers. Knockdown of hPaf1/PD2 in OCSCs resulted in a significant downregulation of CSC and self-renewal markers, and impairment of in vitro tumor sphere (P < 0.05) and colony formation (P = 0.013). Co-immunoprecipitation revealed that OCT3/4 specifically interacts with hPaf1/PD2, and not with other PAF components (Ctr9, Leo1, Parafibromin) in OCSCs, suggesting a complex-independent role for hPaf1/PD2 in OCSC maintenance. Moreover, there was a significant overexpression and co-localization of hPaf1/PD2 with OCT3/4 in OC tissues compared to normal ovary tissues. Our results indicate that hPaf1/PD2 is overexpressed in OCSCs and maintains the self-renewal of OCSCs through its interaction with OCT3/4; thus, hPaf1/PD2 may be a potential therapeutic target to overcome tumor relapse in OC.


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