Acute sensitivity of the oral mucosa to oncogenic K-ras

Injury prevents Ras mutant cell expansion in mosaic skin

Healthy skin is a mosaic of wild-type and mutant clones1,2. Although injury can cooperate with mutated Ras family proteins to promote tumorigenesis3-12, the consequences in genetically mosaic skin are unknown. Here we show that after injury, wild-type cells suppress aberrant growth induced by oncogenic Ras. HrasG12V/+ and KrasG12D/+ cells outcompete wild-type cells in uninjured, mosaic tissue but their expansion is prevented after injury owing to an increase in the fraction of proliferating wild-type cells. Mechanistically, we show that, unlike HrasG12V/+ cells, wild-type cells respond to autocrine and paracrine secretion of EGFR ligands, and this differential activation of the EGFR pathway explains the competitive switch during injury repair. Inhibition of EGFR signalling via drug or genetic approaches diminishes the proportion of dividing wild-type cells after injury, leading to the expansion of HrasG12V/+ cells. Increased proliferation of wild-type cells via constitutive loss of the cell cycle inhibitor p21 counteracts the expansion of HrasG12V/+ cells even in the absence of injury. Thus, injury has a role in switching the competitive balance between oncogenic and wild-type cells in genetically mosaic skin.

Genetically manipulating endogenous Kras levels and oncogenic mutations in vivo influences tissue patterning of murine tumorigenesis

Despite multiple possible oncogenic mutations in the proto-oncogene KRAS, unique subsets of these mutations are detected in different cancer types. As KRAS mutations occur early, if not being the initiating event, these mutational biases are ostensibly a product of how normal cells respond to the encoded oncoprotein. Oncogenic mutations can impact not only the level of active oncoprotein, but also engagement with proteins. To attempt to separate these two effects, we generated four novel Cre-inducible (LSL) Kras alleles in mice with the biochemically distinct G12D or Q61R mutations and encoded by native (nat) rare or common (com) codons to produce low or high protein levels. While there were similarities, each allele also induced a distinct transcriptional response shortly after activation in vivo. At one end of the spectrum, activating the KrasLSL-natG12D allele induced transcriptional hallmarks suggestive of an expansion of multipotent cells, while at the other end, activating the KrasLSL-comQ61R allele led to hallmarks of hyperproliferation and oncogenic stress. Evidence suggests that these changes may be a product of signaling differences due to increased protein expression as well as the specific mutation. To determine the impact of these distinct responses on RAS mutational patterning in vivo, all four alleles were globally activated, revealing that hematolymphopoietic lesions were permissive to the level of active oncoprotein, squamous tumors were permissive to the G12D mutant, while carcinomas were permissive to both these features. We suggest that different KRAS mutations impart unique signaling properties that are preferentially capable of inducing tumor initiation in a distinct cell-specific manner.

Frequent KRAS and HRAS mutations in squamous cell papillomas of the head and neck

Squamous cell papilloma (SCP) is a benign neoplasm of the head and neck. Human papillomavirus (HPV) has been reported to be a tumourigenic factor for SCP. However, not all SCPs are positive for HPV, suggesting that other possible mechanisms are involved in their development. In this study, we examined the mutational status of 51 SCPs using targeted panel sequencing in addition to HPV status using GP5+/GP6+ PCR. HPV DNA was detected in 6 (12%) SCPs, while KRAS and HRAS mutations were detected in 18 (35%) and 17 (33%) SCPs, respectively. Notably, KRAS mutations, HRAS mutations and HPV infection were mutually exclusive. The larynx and trachea (4/7, 57%) were more preferentially infected by HPV than the other sites (2/44, 5%, p = 0.0019) and HPV was associated with multifocal development (4/5, 80%). In contrast, KRAS and HRAS mutations in SCPs were evenly distributed across the anatomical sites and found only in single SCPs. In conclusion, this study demonstrated that HPV was not frequently involved in SCPs and that RAS mutations were more common alterations. In contrast to inverted sinonasal papillomas and oncocytic sinonasal papillomas, SCP may not be a precursor lesion of carcinoma, because these aetiological events in SCP are distinct from squamous cell carcinoma in the same sites.

Sinonasal squamous cell carcinoma and EGFR mutations: a molecular footprint of a benign lesion

AIMS

Molecular targeted therapy against EGFR kinase domain mutations has been successfully established for lung cancer. These mutations have now also been reported in head and neck tumours, particularly in inverted sinonasal papillomas (ISPs). The aim of this study was to clarify the spectrum of EGFR mutations in head and neck squamous cell carcinomas and papillomas.

METHODS AND RESULTS

We examined EGFR mutations in 288 head and neck squamous cell carcinomas and 58 head and neck papillomas or polyps. EGFR mutations were detected in 24 (30%) of 80 sinonasal squamous cell carcinomas (SNSCCs) and in 19 (90%) of 21 ISPs. Notably, 15 (88%) of 17 SNSCCs that developed along with ISPs harboured EGFR mutations in both components, whereas EGFR mutations were detected in nine (14%) of 63 SNSCCs without any papilloma component. Analysis to detect other known driver oncogene mutations - KRAS, BRAF and HER2 - was also performed; none of these mutations was detected in SNSCCs. The other 208 non-sinonasal carcinomas and 37 non-ISP head and neck papillomas or polyps did not harbour EGFR mutations.

CONCLUSIONS

Taken together with the specific involvement of EGFR mutations in ISP, a molecular benign lesion trail suggests that 26 (33%) of 80 SNSCCs developed in association with an ISP. SNSCCs with EGFR mutations may be biologically distinct among head and neck cancers.

Sebaceous lipids are essential for water repulsion, protection against UVB-induced apoptosis and ocular integrity in mice

Sebocytes, which are characterized by lipid accumulation that leads to cell disruption, can be found in hair follicle-associated sebaceous glands (SGs) or in free SGs such as the Meibomian glands in the eyelids. Because genetic tools that allow targeting of sebocytes while maintaining intact epidermal lipids are lacking, the relevance of sebaceous lipids in health and disease remains poorly understood. Using Scd3, which is expressed exclusively in mature sebocytes, we established a mouse line with sebocyte-specific expression of Cre recombinase. Both RT-PCR analysis and crossing into Rosa26-lacZ reporter mice and Kras(G12D) mice confirmed Cre activity specifically in SGs, with no activity in other skin compartments. Importantly, loss of SCD3 function did not cause detectable phenotypical alterations, endorsing the usefulness of Scd3-Cre mice for further functional studies. Scd3-Cre-induced, diphtheria chain A toxin-mediated depletion of sebaceous lipids resulted in impaired water repulsion and thermoregulation, increased rates of UVB-induced epidermal apoptosis and caused a severe pathology of the ocular surface resembling Meibomian gland dysfunction. This novel mouse line will be useful for further investigating the roles of sebaceous lipids in skin and eye integrity.

Immunocompromised and immunocompetent mouse models for head and neck squamous cell carcinoma

Mouse models can closely mimic human oral squamous epithelial carcinogenesis, greatly expand the in vivo research possibilities, and play a critical role in the development of diagnosis, monitoring, and treatment of head and neck squamous cell carcinoma. With the development of the recent research on the contribution of immunity/inflammation to cancer initiation and progression, mouse models have been divided into two categories, namely, immunocompromised and immunocompetent mouse models. And thus, this paper will review these two kinds of models applied in head and neck squamous cell carcinoma to provide a platform to understand the complicated histological, molecular, and genetic changes of oral squamous epithelial tumorigenesis.

Mutation, clonal fitness and field change in epithelial carcinogenesis

Developments in lineage tracing in mouse models have revealed how stem cells maintain normal squamous and glandular epithelia. Here we review recent quantitative studies tracing the fate of individual mutant stem cells which have uncovered how common oncogenic mutations alter cell behaviour, creating clones with a growth advantage that may persist long term. In the intestine this occurs by a mutant clone colonizing an entire crypt, whilst in the squamous oesophagus blocking differentiation creates clones that expand to colonize large areas of epithelium, a phenomenon known as field change. We consider the implications of these findings for early cancer evolution and the cancer stem cell hypothesis, and the prospects of targeted cancer prevention by purging mutant clones from normal-appearing epithelia.

The epidermis comprises autonomous compartments maintained by distinct stem cell populations

The complex anatomy of the epidermis contains multiple adult stem cell populations, but the extent to which they functionally overlap during homeostasis, wound healing, and tumor initiation remains poorly defined. Here, we demonstrate that Lrig1(+ve) cells are highly proliferative epidermal stem cells. Long-term clonal analysis reveals that Lrig1(+ve) cells maintain the upper pilosebaceous unit, containing the infundibulum and sebaceous gland as independent compartments, but contribute to neither the hair follicle nor the interfollicular epidermis, which are maintained by distinct stem cell populations. In contrast, upon wounding, stem cell progeny from multiple compartments acquire lineage plasticity and make permanent contributions to regenerating tissue. We further show that oncogene activation in Lrig1(+ve) cells drives hyperplasia but requires auxiliary stimuli for tumor formation. In summary, our data demonstrate that epidermal stem cells are lineage restricted during homeostasis and suggest that compartmentalization may constitute a conserved mechanism underlying epithelial tissue maintenance.

Single nucleotide polymorphisms of mucosa-associated lymphoid tissue 1 in oral carcinoma cells and gingival fibroblasts

Oral carcinoma patients with inactivation of mucosa-associated lymphoid tissue 1 (MALT1) expression worsen their prognoses. Although the genetic mutation could be responsible for the inactivation, no information is available at present. In the present study, genomic DNA of oral carcinoma cells (HOC313, TSU, HSC2, HSC3, KOSC2, KOSC3, SCCKN, OSC19, Ca9.22, and Ho1u1 cells) and normal gingival fibroblasts (GF12 cells) derived from a Japanese population were amplified by polymerase chain reaction using primer sets spanning MALT1 exons, and nucleotide substitutions were analyzed by the single strand conformation polymorphism analysis. The substitutions were commonly observed in all cells, which express MALT1 at various levels. The substitutions at exons 1 and 9 were located at the 5' untranslated region and replaced (336)Asp to Asn, respectively, and others were positioned at the introns. Among the intronic substitutions, four were matched with the single nucleotide polymorphisms (SNPs) registered at the database. Since all cells were derived from a Japanese population, all substitutions detected are the SNPs. Absence of the carcinoma cell-specific mutation suggests that the inactivation of MALT1 expression but not the mutation promotes oral carcinoma progression.