Expression of Yes-associated Protein in Oral Squamous Cell Carcinoma

INTRODUCTION

Oral cancer, being a serious issue worldwide, has been positioned among the top three types of cancer in the country.¹ Because of social, cultural, topographical aspects, and existence of different addictive practices, the occurrence of oral cancer is very common.² Irrespective of disposal of the latest diagnostic and therapeutic approaches regarding diagnosis of squamous cell carcinoma of oral cavity (OSCC) and its treatment, the survival of these OSCC patients has not revealed much development.³ Millions of people capitulate to OSCC annually.⁴ Being a multifactorial disorder, numerous pathogeneses have been proposed till date explaining the development of OSCC. Understanding the molecular mechanisms of carcinogenesis will offer precious knowledge on diagnosis and prognosis, as well as help in developing a novel therapy. Understanding the biological behavior of cancer is of utmost value to settle on the most apposite therapeutic strategy and ascertain the prognosis of the lesion, which can be facilitated by identification of prognostic markers. Innovative diagnostic techniques like polymerization chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), cell culture, and immunohistochemistry have been recommended to determine prognostic markers in OSCC. YAP is one such prognostic marker that is involved in carcinogenesis of various malignancies, including OSCC.⁵

YAP, a strategic controller of size of the organs, is involved in the Hippo pathway as a nuclear effecter. The Hippo signaling pathway panels the poise among cellular proliferation and apoptosis.⁶ It consists of a regulatory serine–threonine kinase module and a transcriptional module, the kinase module including mammalian STE20-like protein kinase 1 (MST1) and MST2, large tumor suppressor 1 (LATS1) and LATS2, together with the adaptor proteins salvador homologue 1 (SAV1), MOB kinase activator 1A (MOB1A), and MOB1B.⁷ These inhibitory kinase modules regulate tissue growth by suppressing the transcription module such as the YAP-1 (YAP1) and transcriptional coactivator with PDZ-binding motif Tafazzin (TAZ).⁸ YAP is often considered as a mammalian ortholog of Drosophila Yorkie (Yki) that endows with a negative feedback to direct the Hippo pathway. It plays a role as transcriptional coactivator/corepressor in controlling cellular growth, proliferation, and apoptosis. Tumorigenesis and distant metastasis-related activities are augmented via transcriptional enhanced associate domain (TEAD) interaction that is domain by YAP.⁹ YAP1 is shown to regulate biological events like epithelial–mesenchymal transition (EMT), cancer cell migration, and cancer stem cell properties. YAP has also proved to play a major role in cancer cell proliferation and alteration, their migration, and invasion.¹⁰ YAP has been archived as a bonafide oncogene in the diagnosis of cancer with its intensification and overexpression been seen in several human tumors and mouse models of cancer. Minor complexes have been recognized that interrupt the YAP1–TEAD compound or block the binding purpose of WW domains.¹¹ These minor particles characterize principal complexes for the improvement of treatments for cancer patients, who port augmented or overexpressed YAP oncogene.⁵

Clinging to the aforementioned aspects of YAP, we hypothesized that OSCC may show an increased expression of YAP in the tumor cells and the expression may increase with the grade and stage of the cancer. The present article is an attempt to evaluate the expression of YAP in OSCC cells with clinicopathological parameters.

MATERIALS AND METHODS

RESULTS

DISCUSSION

The Hippo signaling pathway that is significantly important in controlling organ growth and development, stem cell function, tumor suppression, and regeneration was first discovered in the 1990s on Drosophila for mutants exhibiting tissue overgrowth.^12–14 The Hippo flagging pathway has an expansive number of mammalian homologues, for example, Lats1/2, Mob1, Mst1/2, and Sav1, in mammalian are homologues of Hpo, Sav, Wts, and Mats, individually; both YAP and TAZ are homologues of Yki.¹⁴ The present investigation was focused on the expression of YAP in OSCC and was aimed to uncover that YAP assumes a part in tumorigenesis and might be helpful as a free prognostic marker in OSCC. In spite of the fact that it stays questionable whether this conduct is because of a tissue-particular capacities of the Hippo pathway or just because of rare investigations of this pathway in different tissues. Significant numbers of studies have shown that the Hippo pathway performs a crucial role in tumor progression. In addition to enhancement of disease cells’ development, down-regulation of the Hippo pathway makes growth cells impervious to some chemotherapeautic drugs.¹⁵ These discoveries raise the likelihood that remedial intercession of the Hippo flagging pathway may enhance momentum treatment methodologies and models and end up being recipient. The significant focuses of the YAP and TAZ are the homologous individual from the TEAD protein family (TEAD1–4) that control cell contact hindrance, epithelial–mesenchymal transformation (EMT), oncogenic alteration, and apoptotic temperance. The association of the TEAD with the TB spaces prompts enactment of downstream quality transcripts, for example, CTGF and Cyr61. To demolish their capacity to advance cell expansion and tumorigenesis, upsetting the official of YAP or TAZ to TEAD by hereditary tack can be utilized as a remedial regime.¹⁶

The present study used immunohistochemistry to compute and evaluate expression criterions of YAP in OSCC, between its different grades and stages, to scrutinize the mantle of this molecule in oral cancer development and progression. In this study, 28 OSCC cases were included with patient’s age ranging from 46–80 years (mean of 60.92 ± 8.17 years). Thyroid carcinoma that shows a strong expression of YAP was used as a positive control. On the one hand, in the present study, YAP expression was assessed in well-differentiated and moderately differentiated grades and all the stages of OSCC. We observed a weak expression of YAP in 73.33% of well-differentiated OSCC, while a strong expression was observed in 26.66% cases for YAP. On the other hand, moderately differentiated OSCC showed a strong expression in 53.84% cases, while a weak expression was seen in 46.15% cases. In a study piloted by Zhang et al.,¹⁷ they perceived increased YAP expression in OSCC samples and deduced that YAP was more recurrently expressed in the invasive margin of the tumor than to its interior. In contrast to our results, Yuan and Tomlinson¹⁸ analyzed the expression of YAP in relation to traditional prophetic indices of breast carcinoma to show no noteworthy correspondence with tumor grade; however, there was a propensity toward superior incidence of loss in the higher grade tumors, with 55.6% (5 of 9) grade I, 30.8% (8 of 26) grade II, and only 36.4% (24 of 66) grade III retaining YAP expression within the neoplastic population. Ge et al.¹⁹ found lower indexed YAP expression with greater tumor grade of the head and neck squamous cell carcinoma (HNSCC) with increased expression at the tumor invasive front. Hiemer et al.⁵ observed the emergence of highly enriched nuclear YAP in areas with severe dysplasia, further supporting our findings. The results suggested that predisposition to OSCC may be related to the dysregulation of YAP localization.

The expression of YAP in different stages of OSCC was also compared in this study. Out of the total cases included in the present study, 66.66% cases of stage I OSCC and 80% cases of stage II showed a weak expression. Of the total cases of stage III OSCC, 61.53% cases had a strong expression for YAP. The single case each of stages IVa and IVb had a weak expression. No such parallel study was found in the literature comparing various stages of OSCC with YAP expression. Hence, this parameter of the study could not be compared. However, Ge et al.¹⁹ observed that nuclear expression of YAP declined with mounting clinical stage in HNSCC.

The expression of YAP in various tumor sizes was compared in OSCC. A strong expression for YAP was observed in one T1 case of OSCC and weak in five cases. Nine cases with T2 demonstrated strong YAP expression, while nine showed weak YAP expression. A strong expression was found in two cases with T3. To the best of our knowledge, no other studies have included a comparison of tumor size and YAP expression in the literature and, thus, we could not compare this parameter as well.

An attempt was made to correspond the YAP expression in different nodal status in metastatic OSCC. A strong association of YAP expression was observed with N1 nodal metastatic OSCC, while a weak expression of YAP was found in N3 metastatic OSCC. Ge et al.¹⁹ have also verified the expression of YAP in the primary HNSCC with nodal metastasis and found an increased cytoplasmic YAP-indexed expression with the occurrence of nodal metastasis in HNSCC.

CONCLUSIONS

In summary, the current study demonstrated that YAP expression significantly increased with successive histologic grades of OSCC, suggesting its possible role as a prognostic marker to detect the severity of OSCC. Taken together our observations indicate that YAP/TAZ contributes in a consequential manner in OSCC oncology. Given that YAP/TAZ are dysregulated during the early onset of OSCC, further discernment of the YAP/TAZ-regulated transcriptional events and amalgamating them to other cancer-related signaling pathways could provide new perspicacity into OSCC. Moreover, novel therapeutic approaches may evolve through the emergence of small molecules duping YAP/TAZ activity, which could help improve the overall threats from this deadly disease. But we counsel future studies on bigger sample size to corroborate our result as our sample size was smaller and we could not include poorly differentiated OSCC in the study group. Future studies are needed to put more cognizances into the role of YAP in prognosticating biological behavior of OSCC.

CLINICAL SIGNIFICANCE

YAP could be exploited as a prognostic marker for nodal metastasis in OSCC cases.

ETHICAL APPROVAL

This article does not contain any studies with human participants or animals performed by any of the authors. All procedures performed in studies were in accordance with the ethical standards of the institutional and/or national research committee.

INFORMED CONSENT

For this type of study, formal consent is not required.

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