Tumor-Initiating Cells Are Enriched in CD44hi Population in Murine Salivary Gland Tumor

Abstract

Tumor-initiating cells (T-ICs) discovered in various tumors have been widely reported. However, T-IC populations in salivary gland tumors have yet to be elucidated. Using the established Pleomorphic Adenoma Gene-1 (Plag1) transgenic mouse model of a salivary gland tumor, we identified CD44high (CD44hi) tumor cells, characterized by high levels of CD44 cell surface expression, as the T-ICs for pleomorphic adenomas. These CD44hi tumor cells incorporated 5-bromo-2-deoxyuridine (BrdU), at a lower rate than their CD44negative (CD44neg) counterparts, and also retained BrdU for a long period of time. Cell surface maker analysis revealed that 25% of the CD44hi tumor cells co-express other cancer stem cell markers such as CD133 and CD117. As few as 500 CD44hi tumor cells were sufficient to initiate pleomorphic adenomas in one third of the wildtype mice, whereas more than 1×104 CD44neg cells were needed for the same purpose. In NIH 3T3 cells, Plag1 was capable of activating the gene transcription of Egr1, a known upregulator for CD44. Furthermore, deletion of sequence 81–96 in the Egr1 promoter region abolished the effect of Plag1 on Egr1 upregulation. Our results establish the existence of T-ICs in murine salivary gland tumors, and suggest a potential molecular mechanism for CD44 upregulation.

Role of CD44 in tumor‐initiating cells of salivary gland pleomorphic adenoma: More than a surface biomarker

“…PLAG1 is involved in embryogenesis, fetal development, and tumorigenesis of various neoplasms (Jakobiec, Stagner, Eagle, Lally, & Krane, ; Wang et al, ; Warren, Turpin, Mark, Smolarek, & Li, ). Several previous studies, including those published by our research group, demonstrate that PLAG1 transgenic mice develop spontaneous PA in the submandibular gland (Declercq et al, ; Shen et al, ; Wang et al, ). This mouse model has become a useful tool to study PA.…”

“…Informed consent was obtained from each patient. The PLAG1 transgenic mice were generated and maintained as previously described (Shen et al, ; Zhao et al, ). All the procedures described were approved by the Animal Use and Care Committee of Shanghai Jiao Tong University School of Medicine.…”

“…CD44 hi cells (which are TICs) account for ~8.6% of the tumor cells. When compared with their CD44 low counterparts, CD44 hi cells not only incorporate5‐bromo‐2‐deoxyuridine (BrdU) at a lower rate and retain BrdU for a long period of time in vitro, but also display enhanced tumorigenicity in vivo (Shen et al, ). However, whether CD44 is critical for the biological function of TICs in PA, and whether CD44 is able to induce the transformation of CD44 low cells into TICs, has yet to be elucidated.…”

A novel in vivo model for evaluating functional restoration of a tissue-engineered salivary gland

“…Most recently, the investigation of these HA binding proteins in the context of the salivary gland has focused on their observed upregulation around tumor sites . These proteins are also observed in cancers of the breast and other tissues, suggesting a role in aberrant, unregulated wound repair.…”

“…7 Most recently, the investigation of these HA binding proteins in the context of the salivary gland has focused on their observed upregulation around tumor sites. [14][15][16] These proteins are also observed in cancers of the breast and other tissues, suggesting a role in aberrant, unregulated wound repair. Therefore, the apparent dual nature of CD44 and RHAMM-as markers of healthy regeneration or as markers of unrestricted aberrant neoplasiareflects the same general function: an interface between the cell and its surrounding matrix.…”