Submitted on March 27, 2008
Revised on July 1, 2008
Accepted on July 8, 2008
Differences in Activity and Phosphorylation of MAPK Enzymes in Esophageal Squamous Cells of GERD Patients with and without Barrett's Esophagus
Hui-Ying Zhang, Xi Zhang, Xi Chen1, Deena Thomas1, Kathy Hormi-Carver2, Frederick Elder3, Stuart Jon Spechler4, and Rhonda F. Souza5*
1 University of Texas Southwestern Medical Center/Dallas VA Medical Center
2 University of Texas Southwestern Medical Center at Dallas
3 University of Texas Southwestern Medical Center
4 Dallas VA Medical Center
5 University of Texas Southwesern Medical Center at Dallas/Dallas VA Medical Center
* To whom correspondence should be addressed. E-mail: rhonda.souza{at}verizon.net.
We hypothesized that, in esophageal squamous epithelial cells, there are differences among individuals in the signal transduction pathways activated by acid reflux that might underlie the development of Barrett's esophagus. To explore that hypothesis, we immortalized non-neoplastic, esophageal squamous cells from GERD patients with (NES-B3T) and without (NES-G2T) Barrett's esophagus, and used those cells to study acid effects on MAPK proteins. During endoscopy in GERD patients with and without Barrett's esophagus, we took biopsy specimens from the distal squamous esophagus to study MAPK proteins before and after esophageal perfusion with 0.1N HCl. We used immunoblotting and Western blotting to study MEK1/2 phosphorylation at two activating sites (serines 217/221), MEK1 phosphorylation at an inhibitory site (threonine 286), and MEK1/2 activity. After acid exposure, both cell lines exhibited increased MEK1/2 phosphorylation at the activating sites; the NES-B3T cells had higher levels of MEK1 phosphorylation at the inhibitory site, however, and only the NES-G2T cells showed an acid-induced increase in MEK1/2 activity. Similarly, in the squamous epithelium of GERD patients with and without Barrett's esophagus, acid perfusion increased MEK1/2 phosphorylation at the activating sites in both patient groups; the Barrett's patients had higher levels of MEK1 phosphorylation at the inhibitory site, however, and only the patients without Barrett's demonstrated an acid-induced increase in ERK1/2 phosphorylation. In esophageal squamous cell lines and biopsies from GERD patients with and without Barrett's esophagus, we have found differences in MAPK pathways activated by acid exposure. We speculate that these differences might underlie the development of Barrett's metaplasia.
