PDX1 homeobox protein expression in pseudopyloric glands and gastric carcinomas

Abstract

Background and aims: Although it has been reported that intestinal metaplasia implicated in gastric carcinogenesis is induced by the ParaHox gene CDX2, it is unclear which genes are responsible for the formation of pseudopyloric glands and whether they play a role in gastric carcinogenesis. Pancreatic-duodenal homeobox 1 (PDX1) is also a ParaHox gene which contributes to the genesis and development of the pancreas, duodenum, and antrum. To clarify its significance for the formation of pseudopyloric glands and gastric carcinogenesis, we investigated expression of PDX1 and mucin in gastric carcinomas and surrounding mucosa.

Methods: Gastric carcinoma tissues from 95 patients were used for immunohistochemical analyses of PDX1, and mucins MUC6 and MUC5AC.

Results: PDX1 was found to be frequently expressed in pseudopyloric glands and intestinal metaplasia. MUC6 was more abundant than MUC5AC in pseudopyloric glands while higher levels of MUC5AC than MUC6 were evident in intestinal metaplasia. The frequency of PDX1 positive reactivity was higher in differentiated type carcinomas (39/43, 90.7%) and T1 carcinomas (42/43, 97.7%) than in undifferentiated type (33/52, 63.5%) and T2-4 (30/52, 57.7%) carcinomas. PDX1 and MUC6 double positive expression was observed in carcinomas, respectively, including the corpus, and also correlated with histological type and depth of invasion. In contrast, no link was apparent between PDX1 and MUC5AC double positive reactivity and histological type.

Conclusion: Our study suggests that PDX1 plays an important role in the development of pseudopyloric glands, and that pseudopyloric glands may reflect a condition associated with gastric carcinogenesis.

Figure 1

Confirmation of anti-pancreatic-duodenal homeobox 1 (PDX1) antibody by western blot analysis. (A) Lane 1: Band was not detected in GT3TKB transfected with pcDNA3.1-PDX1, reacted with pre-immunised serum; lane 2: no band was seen in GT3TKB transfected with mammalian expression vector without PDX1 cDNA, reacted with anti-PDX1 antibody; lane 3: a predicted band was detected in GT3TKB transfected with pcDNA3.1-PDX1, reacted with anti-PDX1 antibody; lanes 4, 5: the band disappeared in GT3TKB transfected with pcDNA3.1-PDX1, reacted with anti-PDX1 antibody treated with 10 and 50 µg of glutathione-S-transferase (GST)-PDX1, respectively; lanes 6, 7: the band did not fade out in GT3TKB transfected with pcDNA3.1-PDX1, reacted with anti-PDX1 antibody treated with 10 and 50 µg of GST, respectively. α-Tubulin was analysed as an internal control. (B) Lane 1: a band appears in extracted proteins from the normal antrum; lanes 2, 3: no band was observed in proteins from the normal corpus and colon, respectively.

Figure 2

Expression of pancreatic-duodenal homeobox 1 (PDX1), pepsinogen I, and mucins MUC6 and MUC5AC in serial sections through pseudopyloric glands. (A) PDX1 is expressed in pseudopyloric glands surrounding carcinoma cells. Arrows indicate PDX1 expression in the nuclei of pseudopyloric gland cells. Arrowheads indicate PDX1 positive carcinoma cells. (B) MUC6 positive reactivity is also apparent. (C) No MUC5AC is expressed in the pseudopyloric glands. (D) The presence of pseudopyloric glands was confirmed by antihuman pepsinogen I monoclonal antibody staining. Original magnification: A, C, 400×; B, D, 200×.

Figure 3

Expression patterns of pancreatic-duodenal homeobox 1 (PDX1) and the mucins MUC6 and MUC5AC in representative serial sections through intestinal metaplasia. (A) PDX1 positive reactivity is located in nuclei along the intestinalised epithelium. (B) No MUC6 expression is seen in intestinal metaplasia. (C) MUC5AC expression is evident in perinuclear portions of cells. Original magnification: 200×.

Figure 4

Pancreatic-duodenal homeobox 1 (PDX1) expression in gastric carcinomas by immunohistochemistry. (A, B) PDX1 positive reactivity is observed in differentiated and undifferentiated types of T1 carcinomas, respectively. (C, D) PDX1 is negative in differentiated and undifferentiated types of T2–4 carcinomas. Original magnification: A, 200×; B–D, 400×.

Figure 5

Comparison of pancreatic-duodenal homeobox 1 (PDX1) with mucin MUC6 and MUC5AC expression in serial sections through gastric carcinomas. (A, B) PDX1 expression is apparent in differentiated and undifferentiated type carcinomas, respectively. (C) PDX1 reactivity is not evident in undifferentiated type carcinoma. (D, G) MUC6 and MUC5AC expression is generally associated with PDX1 in differentiated type carcinoma. (E, F) MUC6 expression is not apparent in undifferentiated type carcinomas. (H, I) MUC5AC is expressed in undifferentiated type carcinomas. Original magnification: A, D, G, 200×; B, C, E, F, H, I, 400×.