The HER4 isoform JM-a/CYT2 relates to improved survival in bladder cancer patients but only if the estrogen receptor α is not expressed

Abstract

Bladder cancer tumors expressing human epidermal growth factor receptor 4 (HER4) demonstrate improved patient survival. HER4 isoforms and estrogen receptor alpha (ER-α) can form chaperone complexes causing cell-proliferation. We wanted to explore if HER4 isoforms and ER-α could correlate to poor prognosis in bladder cancers. We developed mRNA assays for HER4 isoforms (JM-a, JM-b, CYT1, and CYT2) and for ER-α. Expression was analyzed in tumors from 85 bladder cancer patients and compared to overall survival (median follow-up of 5.1 years). ER-α was expressed in 38% (n = 32) of tumors but did not correlate to survival (p = 0.4698). HER4 was expressed in 42% (n = 36) and in all cases as the ER-α binding isoform JM-a. The JM-a isoform can be alternatively spliced to either a CYT1 isoform (JM-a/CYT1) or a CYT2 isoform (JM-a/CYT2). All HER4 expressing tumors expressed the JM-a/CYT2 isoform and half of those (18/36) expressed both isoforms. JM-a/CYT2 expression correlated to improved survival (p = 0.004), but not when ER-α was co-expressed (p = 0.897). Immunohistochemistry revealed protein expression of HER4 and ER-α in tumor cells. Growth of RT4 bladder cancer cells, expressing both JM-a/CYT2 and ER-α was inhibited by the specific ER-α inhibitor raloxifene. Likewise, stable transfection with JM-a/CYT2 inhibited the growth of T24 bladder cancer cells, but only when ER-α was inhibited. Our results demonstrate that HER4 JM-a/CYT2 expressing bladder cancers relate to favorable prognosis when ER-α is not co-expressed. In vitro studies indicate that ER-α inhibition may be a useful treatment for patients with tumors expressing both ER-α and HER4 JM-a/CYT2.

Key Words::

• Bladder cancer
• estrogen receptor alpha
• receptor tyrosine-protein kinase erbB-4
• isoforms
• protein splice variants
• mRNA
• cell line
• Real-time PCR
• cell proliferation

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

We acknowledge the valuable technical assistance from technicians Birgit Mortensen and Marianne Lysdahl (Department of Clinical Biochemistry, Aarhus University Hospital) as well as Lise Strange and Heidi Paulsen (Department of Medical Anatomy, The Panum Institute, Copenhagen). We also thank the Molecular Oncology of the Bladder (MOB) biobank (Skejby, Denmark, collected and maintained under supervision of Torben F. Orntoft and Lars Dyrskjoet) for providing the biopsy samples.