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The role of evolutionarily conserved homeobox-containing HOX genes as transcriptional regulators in the developmental specification of organisms is well known. The contribution of HOX genes involvement in oral cancer phenotype has yet to be fully ascertained. TCGA-HNSC HTSeq-counts and clinical data were retrieved from the GDC portal for oral cavity neoplasms. GEO datasets (GSE72627, GSE30784, GSE37991) were accessed and analyzed using GEO2R. Differential HOX gene expression was profiled using the DESeq2 R package with a log2 fold change cut-off (− 1 and + 1) and Benjamini–Hochberg p-adjusted value at ≤ 0.01. Gene set over-representation analysis and semantic analysis associated with the disease ontology was performed using the ClusterProfiler R package, and pathway over-representation analysis was performed using IMPaLa. HOX protein interaction network was constructed using the Pathfind R package. HOX phenotype associations were performed using Mammalian Phenotype Ontology, Human Phenotype Ontology, PhenGenI associations, Jensen tissues, and OMIM entries. Drug connectivity mapping was carried out with Dr. Insight R package. HOXA2 was upregulated in oral dysplasia but silenced during tumor progression. Loss of HOXB2 expression was consistent in the potentially malignant oral lesions as well as in the primary tumor. HOXA7, HOXA10, HOXB7, HOXC6, HOXC10, HOXD10, and HOXD11 were consistently upregulated from premalignancy to malignancy and were notably associated with risk factors. Overrepresentation analysis suggested HOXA10 was involved in the transcriptional misregulation contributing to the oral cancer phenotype. HOX genes subnetwork analysis showed crucial interactions with cell cycle regulators, growth responsive elements, and proto-oncogenes. Phenotype associations specific to the oral region involving HOX genes provide intrinsic cues to tumor development. The 5′ HOX genes were aberrantly upregulated during oral carcinogenesis reflecting their posterior prevalence.

HOX genes are members of the homeotic transcription factor family, organized into four paralogous clusters. HOX complexes are believed to have arisen by genome-wide duplications during evolution. In humans, there are about 200 homeobox genes of which 39 are HOX genes, which are segregated onto four chromosomes, HOXA -7p15, HOXB -17q21.2, HOXC -12q13, and HOXD -2q31 (Figure 1). 1,2 The protein product of the HOX gene is a transcription factor that contains a conserved homeodomain region. 2 The homeodomain consists of the helix-turn-helix protein motif responsible for sequence-specific DNA binding. HOX genes are the pivotal regulators of growth and development. They regulate events such as differentiation, metabolism, apoptosis, autophagy, and their deregulation leads to various disorders and diseases including cancer. 3

Purpose: Evolutionarily conserved homeobox-containing HOX genes as transcriptional regulators in the developmental specification of organisms is well known. The contribution of HOX genes involvement in oral cancer phenotype has yet to be fully ascertained.Methods: GEO datasets (GSE72627, GSE30784, GSE37991) were accessed and analyzed using GEO2R. TCGA-HNSC HTSeq-counts and clinical data were retrieved from the GDC portal for oral cavity neoplasms. Differential HOX gene expression was profiled using the DESeq2 R package with a log2 fold change cut-off (-1 and +1) and Benjamini-Hochberg p-adjusted value at <0.01. Gene set over-representation analysis and semantic analysis associated with the disease ontology were performed using ClusterProfiler R package and pathway over-representation analysis was performed using IMPaLa. HOX protein interaction network was constructed using the Pathfind R package. HOX phenotype associations were performed using Mammalian Phenotype Ontology, Human Phenotype Ontology, PhenGenI associations, Jensen tissues, and OMIM entries. Drug connectivity mapping was carried out with Dr. Insight R Package.Results: HOXB2 and HOXA5 genes were upregulated in oral dysplasia but silenced during tumor progression. Loss of HOXB2 expression was consistent through potentially malignant dysplastic oral lesions (PMOL) to primary tumor formation. HOXA10, HOXB7, HOXC6, HOXC10 and HOXD10 showed consistent upregulation from premalignancy to malignancy and were notably associated with risk factors. Overrepresentation analysis suggested HOXA10 was involved in the transcriptional misregulation leading to oral cancer phenotype. HOX subnetwork analysis showed crucial interactions with cell cycle regulators, growth responsive elements, and proto-oncogenes.Conclusion: Phenotype associations specific to the oral region involving HOX genes provide intrinsic cues to tumor development. The 5’ HOX genes were aberrantly deregulated which reflects their posterior prevalence during oral carcinogenesis.

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