Increased expression of Yes-associated protein 1 in hepatocellular carcinoma with stemness and combined hepatocellular-cholangiocarcinoma

Abstract

Combined hepatocellular-cholangiocarcinoma (cHC-CC) and some hepatocellular carcinomas (HCCs) express stemness-related markers, such as epithelial adhesion molecule (EpCAM) and keratin 19 (K19), the expression of which has been reported to be associated with more aggressive behavior therein than in HCCs without. Yes-associated protein 1 (YAP1), a potential oncogene, is known to promote stem cell proliferation. In the present study, YAP1 expression and clinicopathological features were evaluated and compared among three groups comprising 36 HCCs that expressed both EpCAM and K19, 64 HCCs that did not express EpCAM and K19, and 58 cHC-CCs, which consisted of 38 cases of the classical type and 20 cases of the intermediate-cell subtype. YAP1 expression was more frequently noted in EpCAM(+)/K19(+) HCCs (55.6%) and in cHC-CCs (67.2%) than in EpCAM(-)/K19(-) HCCs (17.2%) (P<0.001 for both). In cHC-CCs, YAP1 expression was observed in 63% of classical type cHC-CCs and in 75% of the intermediate subtype; moreover, such expression was correlated with poorer histological differentiation (P = 0.017) and was more frequently noted in transition zones than in HCC areas (P = 0.060). Disease-free and overall survival showed a statistically significant difference among the three groups: disease-free survival was highest for EpCAM(-)/K19(-) HCCs and lowest for cHC-CCs, with EpCAM(+)/K19(+) HCCs falling in between (P<0.05). Overall survival rate was lower in HCCs and cHC-CCs with YAP1 expression compared to those without (P = 0.05), whereas disease-free survival showed no significant difference according to YAP1 expression. Increased YAP1 expression was more frequently found in cHC-CCs and HCCs with stemness than in HCCs without, and a YAP1 pathway is suggested to be involved in the obtainment stemness characteristics in HCCs and cHC-CCs.

Figure 1. EpCAM and K19 expression in hepatocellular carcinoma (HCC).

(A-D) HCC expressing both EpCAM and K19. The expression of EpCAM was mainly membranous, and K19 showed cytoplasmic expression in tumor cells. Nuclear expression of YAP1 was noted. (E-H) HCC without expression of both EpCAM and K19. There was no nuclear expression of YAP1. (Original magnification, ×200).

Figure 2. YAP1 expression in combined hepatocellular cholangiocarcinoma (cHC-CC).

(A-F) Pathological features and YAP1 expression are shown in each component of classical type combined hepatocellular cholangiocarcinoma, including a hepatocellular carcinoma (HCC) area (A, B), a cholangiocarcinoma (CC) area (C, D), and a transitional zone (E, F). YAP1 expression is evident in the nuclei of tumor cells in CC areas (D) and transitional zones (F) in contrast to weak nulcear YAP1 expression in HCC areas (B). (G-H) Intermediate subtype of cHC-CC with stem cell features showing strong nuclear YAP1 expression. (Original magnification, ×200).

Figure 3. Kaplan–Meier's plot analysis for disease-free survival and overall survival in HCCs and combined hepatocellular-cholangiocarcinomas (cHC-CCs).

Kaplan–Meier's plot analysis for disease-free survival (A) and overall survival (B) showing a significant difference among EpCAM(−)/K19(−) HCCs, EpCAM(+)/K19(+) HCCs, and cHC-CCs. Overall survival was relatively worse in HCCs and cHC-CCs with YAP1 expression (D), whereas there was no significant difference in disease-free survival between the two groups.