Abstract 414A: m6A reader proteins, YTHDF1 and YTHDF2, are associated with better patients' survival and inflamed tumor immune microenvironment in non-small lung cancer
Authors: Tsuchiya Kazuo , Yoshimura Katsuhiro , Inoue Yusuke , Iwashita Yuji , Yamada Hidetaka , Kawase Akikazu , Tanahashi Masayuki , Ogawa Hiroshi , Funai Kazuhito , Shinmura Kazuya , Suda Takafumi , Sugimura Haruhiko 
Published: September 2020

Background: The human YTH domain family protein (YTHDF) family is RNA binding protein which specifically recognizes N6-methyladenosine (m6A), and exerts distinct roles in eukaryocytes; YTHDF1 promotes the translation of m6A modified mRNAs collaborating with initiation factors, and YTHDF2 reduces the stability of the m6A-modified transcripts. The previous reports showed YTHDF1/2 are associated with cancer progressiveness in colorectal cancers and prostate cancers. In contrast, YTHDF2 is reported to act as an anti-tumoral function in hematologic malignancies. Further, a recent investigation showed that YTHDF1 interacted with the tumor immune microenvironment and modulate an anti-tumor immune response. However, the clinical relevance of YTHDF1/2 in non-small cell lung cancers (NSCLCs) has yet to be elucidated fully.

Method: We evaluated the protein expression levels of YTHDF1/2 in the 603 resected NSCLCs, including 392 adenocarcinomas and 170 squamous cell carcinomas by immunohistochemistry. The tumor expression levels were assessed by H-scores that ranged from 0 to 300. We also assessed the four subsets of lymphocytes, PD-1+, CD8+, Foxp3+, and CD45RO+ as tumor-infiltrating lymphocytes (TILs), in tumor nest and surrounding stroma separately. TILs were counted under high-power fields (× 200). Their associations with patients' characteristics and survival were retrospectively explored. We additionally validated the prognostic association of YTHDF1/2 using the mRNA expression data derived from the TCGA dataset.

Result: The median age was 68 years old (range, 23-88) and 414 (68.7%) patients were male. Significantly higher expressions of YTHDF1/2 was observed in tumors with a lower grade of the pathological stage. They were also significantly associated with adenocarcinoma histology. Multivariate Cox regression analyses demonstrated that YTHDF2 were independent favorable prognostic factors for overall survivals (HR, 0.674; 95% CI, 0.455-0.998) and YTHDF1/2 were independent favorable prognostic factors recurrence-free survivals (HR, 0.755; 95%CI, 0.572-0.998 for YTHDF1, and HR, 0.679; 95%CI, 0.500-0.921 for YTHDF2). Regarding stromal TILs, the numbers of individual TILs significantly increased in high YTHDF2 tumors. All subsets of TILs except CD8+ were also significantly greater in high YTHDF1 tumors. In tumor nest, the numbers of Foxp3+ were also significantly prominent in high YTHDF2 tumors, but neither kind of TILs was associated with YTHDF1 expression. TCGA dataset showed that YTHDF1/2 expressions were significantly higher in tumor tissue than in corresponding non-tumor tissues. High YTHDF2 mRNA expression was also a favorable prognostic indicator, but YTHDF1 was not.

Conclusion: High YTHDF1/2 expressions were favorable prognostic factors in patients with NSCLC. They were also significantly associated with several kinds of TILs. YTHDF2 and part of YTHDF1 might not only exhibit anti-tumor activity but also relate to the inflamed tumor microenvironment.

Citation Format: Kazuo Tsuchiya, Katsuhiro Yoshimura, Yusuke Inoue, Yuji Iwashita, Hidetaka Yamada, Akikazu Kawase, Masayuki Tanahashi, Hiroshi Ogawa, Kazuhito Funai, Kazuya Shinmura, Takafumi Suda, Haruhiko Sugimura. m6A reader proteins, YTHDF1 and YTHDF2, are associated with better patients' survival and inflamed tumor immune microenvironment in non-small lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 414A.