Objective:Flotillin-2(FLOT2)is a prototypical oncogenic and a potential target for cancer therapy.However,strategies for targeting FLOT2 remain undefined.Post-translational modifications are crucial for regulating protein stability,function,and localization.Understanding the mechanisms and roles of post-translational modifications is key to developing targeted therapies.This study aims to investigate the regulation and function of lysine acetylation of FLOT2 in nasopharyngeal carcinoma,providing new insights for targeting FLOT2 in cancer intervention. Methods:The PhosphoSitePlus database was used to analyze the lysine acetylation sites of FLOT2,and a lysine acetylation site mutation of FLOT2[FLOT2(K211R)]was constructed.Nasopharyngeal carcinoma cells were treated with histone deacetylase(HDAC)inhibitor trichostatin A(TSA)and Sirt family deacetylase inhibitor nicotinamide(NAM).TSA-treated human embryonic kidney(HEK)-293T were transfected with FLOT2 mutant plasmids.Co-immunoprecipitation(Co-IP)was used to detect total acetylation levels of FLOT2 and the effects of specific lysine(K)site mutations on FLOT2 acetylation.Western blotting was used to detect FLOT2/FLAG-FLOT2 protein expression in TSA-treated nasopharyngeal carcinoma cells transfected with FLOT mutant plasmids,and real-time reverse transcription PCR(real-time RT-PCR)was used to detect FLOT2 mRNA expression.Nasopharyngeal carcinoma cells were treated with TSA combined with MG132 or chloroquine(CQ)to analyze FLOT2 protein expression.Cycloheximide(CHX)was used to treat HEK-293T cells transfected with FLAG-FLOT2(WT)or FLAG-FLOT2(K211R)plasmids to assess protein degradation rates.The BioGrid database was used to identify potential interactions between FLOT2 and HDAC6,which were validated by Co-IP.HEK-293T cells were co-transfected with FLAG-FLOT2(WT)/FLAG-FLOT2(K211R)and Vector/HDAC6 plasmids,and grouped into FLAG-FLOT2(WT)+Vector,FLAG-FLOT2(WT)+HDAC6,FLAG-FLOT2(K211R)+Vector,and FLAG-FLOT2(K211R)+HDAC6 to analyze the impact of K211R mutation on total lysine acetylation levels.In 6-0B cells,overexpression of FLOT2(WT)and FLOT2(K211R)was performed,and the biological functions of FLOT2 acetylation site mutants were assessed using cell counting kit-8(CCK-8),colony formation,and Transwell invasion assays. Results:The PhosphoSitePlus database indicated that FLOT2 has an acetylation modification at the K211 site.Co-IP confirmed significant acetylation of FLOT2,with TSA significantly increasing overall FLOT2 acetylation levels,while NAM had no effect.Mutation at the K211 site significantly reduced overall FLOT2 acetylation,unaffected by TSA.TSA decreased FLOT2 protein expression in nasopharyngeal carcinoma cells without affecting FLOT2 mRNA levels or FLOT2(K211R)protein expression in transfected cells.The degradation rate of FLOT2(K211R)protein was significantly slower than that of FLOT2(WT).The proteasome inhibitor MG132 prevented TSA-induced FLOT2 degradation,while the lysosome inhibitor CQ did not.BioGrid data suggested a potential interaction between FLOT2 and HDAC6,confirmed by Co-IP.Knockdown of HDAC6 in nasopharyngeal carcinoma cells significantly increased FLOT2 acetylation;co-transfection of HDAC6 and FLAG-FLOT2(WT)significantly decreased total lysine acetylation levels,whereas co-transfection of HDAC6 and FLAG-FLOT2(K211R)had no effect.Knockdown of HDAC6 significantly reduced FLOT2 protein levels without affecting mRNA levels.MG132 prevented HDAC6-knockdown-induced FLOT2 degradation.Knockdown of HDAC6 significantly accelerated FLOT2 degradation.Nasopharyngeal carcinoma cells transfected with FLOT2(K211R)showed significantly higher proliferation and invasion than those transfected with FLOT2(WT). Conclusion:The K211 site of FLOT2 undergoes acetylation modification,and HDAC6 mediates deacetylation at this site,inhibiting proteasomal degradation of FLOT2 and maintaining its stability and tumor-promoting function in nasopharyngeal carcinoma.

Objective: To analyze the clinical value of real-time PCR for virus detection in the diagnosis and treatment of patients after allo-HSCT who had no infection evidence of pneumonia using routine pathogen detection panel. Methods: The clinical data of 71 episodes with acute lung injury from May 2015 to March 2017 after allo-HSCT in hematology department of Peking University People’s Hospital (PKUPH) were retrospectively analyzed. PCR for virus detection and other routine pathogen detection tests were performed on bronchoalveolar lavage fluid (BALF) samples. Results: Among 71 episodes with acute lung injury, a total of 15 patients were diagnosed as lower respiratory tract disease merely associated with virus (detection rate of 21.13%) , 19 episodes were absent of lower respiratory tract infection. The median time from allo-HSCT to the occurrence of lung injury were 176 (49-1 376) d and 196 (57-457) d respectively (z=-0.191, P=0.864) . There were no statistical differences for baseline characteristics and clinical features between two groups. The 100-day attributable mortalities were 13.3% (2/15) and 26.3% (5/19) (χ²=0.864, P=0.426) . Patients with low-dose steroids treatment had favorable outcome than those with high-dose steroids treatment (the dose of methylprednisolone ≥250 mg/d as standard) [4.2% (1/24) vs 60.0% (6/10) ]. In patients with detectable virus in BALF, 2 patients died with early high-dose steroids treatment, while 11 patients survived with no steroids treatment or late application. Conclusions Virus infection should be considered in post-HSCT pneumonia patient with negative result using routine pathogen detection panel. Expanding virus detection panel by PCR in BALF could increase diagnostic precision and might be instructive to treatment.