Bacterial colonization leads to the colonic secretion of RELM beta/FIZZ2, a novel goblet cell-specific protein

Background & Aims: Goblet cells are highly polarized exocrine cells found throughout the small and large intestine that have a characteristic morphology due to the accumulation of apical secretory granules. These granules contain proteins that play important physio-logic roles in cellular protection, barrier function, and proliferation. A limited number of intestinal goblet cell-specific proteins have been identified. In this study, we investigate the expression and regulation of RELMbeta, a novel colon-specific gene. Methods: The regulation of RUMP messenger RNA expression was determined in LS174T, Caco-2, and HT-29 cell lines in response to stimulation with interleukin 13 and lipopolysaccharide. Quantitative reverse-transcription polymerase chain reaction, immunoblots, and immunohistochemistry were used to examine the expression of RELMbeta in BALB/c and C.B17.SCID mice housed in conventional, germfree, and gnotobiotic environments. Results: Messenger RNA for RELMbeta is restricted to the undifferentiated, proliferating colonic epithelium. Immunohistochemistry shows that this protein is expressed in goblet cells located primarily in the distal half of the colon and cecum with lower levels detectable in the proximal colon. High levels of RELMbeta can be detected in the stool of mice and humans, where it exists as a homodimer under nonreducing conditions. Interestingly, the secretion of RELMbeta is dramatically reduced in germ-free mice. Furthermore, introduction of germ-free mice into a conventional environment results in enhanced expression and robust secretion of RELMbeta within 48 hours. Conclusions: These studies define a new goblet cell-specific protein and provide the first evidence that colon-specific gene expression can be regulated by colonization with normal enteric bacteria.