Risk factors for esophageal cancer: emphasis on infectious agents.

Risk factors for esophageal cancer include genetic factors (such as tylosis) and infectious agents. A variety of organisms have been implicated in esophageal carcinogenesis, either directly or indirectly. In this review, we explore the normal esophageal flora and how it may be controlled, and also the variety of organisms that may affect esophageal carcinogenesis, either directly or indirectly. The organisms with potential direct effects in squamous cell carcinoma include human papillomavirus (HPV), Epstein-Barr virus, and polyoma viruses. Interestingly, HPV is now implicated in esophageal adenocarcinoma (EAC), not in its initiation but in the development of dysplasia, in which HPV33 in particular has been associated. Indirectly, Helicobacter pylori has been associated with EAC by, initially, causing increased acid secretion that increases acid reflux, and by reducing lower esophageal sphincter pressure, which increases gastroesophageal reflux; the latter increases the risk of Barrett's esophagus, and hence EAC. Conversely, subsequent atrophic gastritis may normalize that risk.

RHBDF2 mutations are associated with tylosis, a familial esophageal cancer syndrome.

Tylosis esophageal cancer (TOC) is an autosomal-dominant syndrome characterized by palmoplantar keratoderma, oral precursor lesions, and a high lifetime risk of esophageal cancer. We have previously localized the TOC locus to a small genomic interval within chromosomal region 17q25. Using a targeted capture array and next-generation sequencing, we have now identified missense mutations (c.557T>C [p.Ile186Thr] and c.566C>T [p.Pro189Leu] in RHBDF2, which encodes the inactive rhomboid protease RHBDF2 (also known as iRhom2), as the underlying cause of TOC. We show that the distribution of RHBDF2 in tylotic skin is altered in comparison with that in normal skin, and immortalized tylotic keratinocytes have decreased levels of total epidermal growth factor receptor (EGFR) and display an increased proliferative and migratory potential relative to normal cells, even when normal cells are stimulated with exogenous epidermal growth factor. It would thus appear that EGFR signaling is dysregulated in tylotic cells. Furthermore, we also show an altered localization of RHBDF2 in both tylotic and sporadic squamous esophageal tumors. The elucidation of a role of RHBDF2 in growth-factor signaling in esophageal cancer will help to determine whether targeting this pathway in chemotherapy for this and other squamous cell carcinomas will be effective.

Down-regulation of the cytoglobin gene, located on 17q25, in tylosis with oesophageal cancer (TOC): evidence for trans-allele repression.

Tylosis (focal non-epidermolytic palmoplantar keratoderma) is an autosomal dominant skin disorder that is associated with the early onset of squamous cell oesophageal cancer (SCOC) in three families. Our previous linkage and haplotype analyses have mapped the tylosis with oesophageal cancer (TOC) locus to a 42.5 kb region on chromosome 17q25 that has also been implicated in the aetiology of sporadically occurring SCOC from a number of different geographical populations. Oesophageal cancer is one of the 10 leading causes of cancer mortality worldwide. No inherited disease-causing mutations have been identified in the genes located in the 42.5 kb minimal region. We now show that cytoglobin gene expression in oesophageal biopsies from tylotic patients is dramatically reduced by approximately 70% compared with normal oesophagus. Furthermore, both alleles are equally repressed. Given the autosomal dominant nature of the disease, these results exclude haploinsufficiency as a mechanism of the disease and instead suggest a novel trans-allele interaction. We also show that the promoter is hypermethylated in sporadic oesophageal cancer samples: this may constitute the 'second hit' of a gene previously implicated in this disease by allelic imbalance studies.

Structural organization of cornified cell envelopes and alterations in inherited skin disorders.

The cornified cell envelope is a highly insoluble and extremely tough structure formed beneath the cell membrane during terminal differentiation of keratinocytes. Its main function is to provide human skin with a protective barrier against the environment. Sequential cross-linking of several integral components catalyzed by transglutaminases leads to a gradual increase in the thickness of the envelope and underscores its rigidity. Key structural players in this cross-linking process include involucrin, loricrin, SPRRs, elafin, cystatin A, S100 family proteins, and some desmosomal proteins. The recent identification of genetic skin diseases with mutations in the genes encoding some of these proteins, including transglutaminase 1 and loricrin, has disclosed that abnormal cornified cell envelope synthesis is significantly involved in the pathophysiology of certain inherited keratodermas and reflects perturbations in the complex, yet highly orderly process of cornified cell envelope formation in normal skin biology.