Abstract
The human epidermal growth factor (EGF) receptor (HER) family consists of four receptors that bind to ligands sharing an EGF-like motif. The HER family of receptor tyrosine kinases and their ligands (EGF family) are known to play a significant role in gastrointestinal cancer. In particular, the EGF receptor, HER1, is one of the main candidates for the molecular-targeted therapy of colon cancer, and HER2 is a candidate for the treatment of gastric cancer which overexpresses HER2. In contrast, the role of the HER and EGF families in malignant lymphoma has not been fully elucidated. In this study, we investigated the expression and function of the HER and EGF families in lymphoma cell lines and tumor samples. Reverse transcription polymerase chain reaction revealed that the ligands for HER1 were mainly expressed in gastric cancer and colon cancer cell lines, but not in lymphoma cell lines. On the other hand, the EGF family member, neuregulin (NRG) 4, was highly expressed in lymphoma cell lines. Immunohistochemical analyses of malignant lymphoma clinical samples revealed that NRG4 and HER4 were mainly expressed in mucosa-associated lymphoid tissue (MALT) and follicular lymphoma. Immunoprecipitation of Raji and Daudi cell lines revealed that recombinant NRG4 induced the tyrosine phosphorylation of HER4. Additionally, recombinant NRG4 activated the proliferation of lymphoma cell lines. These findings suggest that the NRG4-HER4 axis plays a major role in the proliferation of malignant lymphoma cells in the gastrointestinal tract.
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