Granulin, a novel STAT3-interacting protein, enhances STAT3 transcriptional function and correlates with poorer prognosis in breast cancer.

Jennifer E Yeh,Andrea Richardson,Simion Kreimer,David A Frank,Hannah Krystal,Alexander R Ivanov,Sarah R Walker,Megan M Emori

doi:10.18632/genesandcancer.58

Abstract

Since the neoplastic phenotype of a cell is largely driven by aberrant gene expression patterns, increasing attention has been focused on transcription factors that regulate critical mediators of tumorigenesis such as signal transducer and activator of transcription 3 (STAT3). As proteins that interact with STAT3 may be key in addressing how STAT3 contributes to cancer pathogenesis, we took a proteomics approach to identify novel STAT3-interacting proteins. We performed mass spectrometry-based profiling of STAT3-containing complexes from breast cancer cells that have constitutively active STAT3 and are dependent on STAT3 function for survival. We identified granulin (GRN) as a novel STAT3-interacting protein that was necessary for both constitutive and maximal leukemia inhibitory factor (LIF)induced STAT3 transcriptional activity. GRN enhanced STAT3 DNA binding and also increased the time-integrated amount of LIF-induced STAT3 activation in breast cancer cells. Furthermore, silencing GRN neutralized STAT3-mediated tumorigenic phenotypes including viability, clonogenesis, and migratory capacity. In primary breast cancer samples, GRN mRNA levels were positively correlated with STAT3 gene expression signatures and with reduced patient survival. These studies identify GRN as a functionally important STAT3-interacting protein that may serve as an important prognostic biomarker and potential therapeutic target in breast cancer.

Highlights

Breast cancer is the most frequently diagnosed cancer and second leading cause of cancer death in American women, accounting for about 230,000 new cases and 40,000 deaths per year [1]
Since cancer is associated with aberrant gene expression patterns, increasing attention has been focused on transcription factors like signal transducer and activator of transcription 3 (STAT3) which lies at the convergence points of many oncogenic signaling pathways
Because GRN was detected in two independent experimental replicates from two breast cancer cell lines with constitutively active STAT3, it was selected for further analysis

Summary

Introduction

Breast cancer is the most frequently diagnosed cancer and second leading cause of cancer death in American women, accounting for about 230,000 new cases and 40,000 deaths per year [1]. TNBCs represent a major cancer health disparity as they occur more frequently and with higher mortality rates in young African-American and Hispanic women [3]. STAT3 is one of a family of transcription factors that mainly reside in the cytoplasm until activated by phosphorylation on a conserved tyrosine residue 705 (PY-STAT3) by growthfactor receptor tyrosine kinases, cytokine-receptorassociated Janus kinases (JAKs), or non-receptor tyrosine kinases [4]. Unphosphorylated STAT3 (U-STAT3) can form dimers and shuttle into the www.impactjournals.com/Genes&Cancer nucleus [5, 6], tyrosine phosphorylation enhances STAT3 dimerization and translocation into the nucleus where it regulates genes involved in cell proliferation, differentiation, survival, and angiogenesis. Cancer cells, including TNBC cells, frequently have inappropriate constitutive activation of STAT3, and can be dependent on STAT3 activity for survival [7]. Aside from its involvement in transcriptional regulation, STAT3 has been reported to play a role in the mitochondrial electron transport chain [9, 10] and microtubule dynamics [13, 14]

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Conclusion