Transglutaminase 2 Is a Direct Target Gene of YAP/TAZ—Letter

We read with great interest the recent article by Fisher and colleagues showing that transglutaminase 2 (TG2) activates YAP in the ECS cells (1). We noticed that, in Fig. 4A in ref. 1, overexpression of the constitutive active YAP (YAP^S127A) did not increase TG2 expression in the SCC13 cells. However, this could be due to high basal expression level of YAP or due to relatively low transfection efficiency. We observed that the Western blot analysis of YAP (in Fig. 4A in ref. 1) only showed a weak increase in YAP protein level after transfection, although a clear FLAG signal was observed, indicating that YAP was not significantly overexpressed.

Our data indicate that TG2 levels are significantly increased upon YAP^S127A and TAZ^4SA overexpression (Fig. 1A–C). The expression of TG2 was inhibited by high cell density (Fig. 1D). Knockdown of YAP/TAZ dramatically decreased TG2 expression in multiple cell lines, including pharynx squamous cell carcinoma cell line FaDu (Fig. 1E). Our analysis of the published chromatin immunoprecipitation (ChIP) sequencing datasets of YAP and TEAD further demonstrated that YAP and TEAD directly bind to the promoter region of TG2 gene in multiple cell lines (Fig. 1F), which was confirmed by ChIP-qPCR (Fig. 1G). Furthermore, the gene coexpression analysis of CCLE dataset showed that the mRNA levels of TG2 positively correlated with multiple known downstream target genes of YAP/TAZ, such as CTGF, CYR61, AXL, ANKRD1, LATS2, and AMOTL2, as well as with the expression levels of YAP/TAZ (Fig. 1H). Treatment with TG2 inhibitor significantly inhibited the growth of the MCF10A cells expressing YAP^S127A in the 3D culture (Fig. 1I). Taken together, these data indicate that TG2 is a direct target gene of YAP/TAZ and plays a vital role in the malignant transformation induced by YAP/TAZ.

TG2 is a multifunctional protein that is overexpressed in multiple cancers and its expression levels positively correlate with metastasis and poor prognosis (2). Interestingly, TG2 is an activator of NF-κB and is also a direct target gene of NF-κB (3). It has been shown that knockdown of TG2 inhibits YAP activity (1, 4). Here, in various cell lines, we show that TG2 is a direct target gene of YAP/TAZ; by upregulating TG2 expression, YAP/TAZ probably also forms a positive feedback loop and amplifies oncogenic programs. TG2 has been a promising therapeutic target for many diseases, including cancer (5). Our results suggest that inhibition of TG2 could be a potent therapeutic strategy for the YAP/TAZ–active cancers.

See the Response, p. 4736