Objective To investigate the expression of DnaJ heat shock protein family member C9(DNAJC9), methylation, prognosis in lung adenocarcinoma (LUAD) and its relation with immune invasion.

Methods The expression and clinical data of LUAD in Cancer Genome Atlas (TCGA) were used to analyze the differential expression of DNAJC9 and its prognostic value. Immunohistochemical method was used to detect the expression of DNAJC9 protein in cancer tissues and adjacent normal tissues of 40 LUAD patients. The methylation sites of DNAJC9 promoter region were analyzed using UALCAN and TCGA Wanderer databases. The correlation between DNAJC9 expression and the level of LUAD immune cell infiltration was analyzed by TIMER database and single sample Gene Set Enrichment Analysis (ssGSEA). The proteins interacting with DNAJC9 were analyzed by String database. Finally, FUNRICH enrichment analysis tool was used for functional enrichment analysis of these genes.

Results The expression of DNAJC9 in LUAD tissues was significantly higher than that in normal tissues (P < 0.01). Immunohistochemistry showed that the expression rate of DNAJC9 protein in LUAD tissues was 80.0%(32/40), which was higher than 45.0% (18/40) in para-cancer tissues(P < 0.05). The overall survival rate, disease-free survival rate and progression-free survival rate of patients with high expression of DNAJC9 were significantly lower than those with low expressions (P < 0.05). The expression of DNAJC9 was significantly correlated with the presence of TP53 mutation (P < 0.05). The methylation level of the promoter region of DNAJC9 gene in tumor tissues was lower than that in normal tissues (P < 0.05), and the methylation sites associated with the expression of the gene sequence were negatively correlated with their expression level(P < 0.05). The expression of DNAJC9 was correlated with the immune infiltration level. Protein interaction network analysis showed that Minichromosome Maintenance Complex Component 6 (MCM6), Ribonucleotide Reductase Catalytic Subunit M1(RRM1), Nuclear Autoantigenic Sperm Protein(NASP), Flap Structure-Specific Endonuclease 1(FEN1), Deoxyuridine Triphosphatase(DUT), Replication Factor C Subunit 4(RFC4), Family With Sequence Similarity 149 Member B1(FAM149B1), MutS Homolog 2(MSH2), Structural Maintenance Of Chromosomes 2(SMC2), Minichromosome Maintenance Complex Component 2(MCM2) proteins had significant interactions with DNAJC9. Pathway enrichment analysis showed that these genes were involved in DNA synthesis, G2/M checkpoint signaling and various carcinogenic processes.

Conclusion The hypommethylation level of DNAJC9 leads to high expression of DNAJC9 in LUAD tissues. Its high expression is an unfavorable prognostic factor of LUAD and is associated with immune cell invasion.