Effects of HIV-1 Tat protein on ion secretion and on cell proliferation in human intestinal epithelial cells.
OBJECTIVE
Severe diarrhea and enteropathy of unknown origin are frequent in patients infected with human immunodeficiency type 1 virus (HIV-1). The HIV-1 transactivating factor protein (Tat) is a key factor in the pathogenesis of acquired immunodeficiency syndrome. We investigated whether Tat could directly induce ion secretion and cell damage in enterocytes.


METHODS
Electrical parameters (ion transport studies) were measured in Caco-2 cell monolayers and in human colonic mucosa specimens mounted in Ussing chambers. The effect of Tat on intestinal mucosa integrity was determined by monitoring the transepithelial electrical resistance of Caco-2 cell monolayers. (3)H-thymidine incorporation and cell count were used to evaluate the effect of Tat on cell growth. Intracellular calcium concentrations were measured at the single-cell level using microfluorometry technique.


RESULTS
Tat protein induced ion secretion in Caco-2 cells and in human colonic mucosa similar to that induced by bacterial enterotoxins. It also significantly prevented enterocyte proliferation. In both instances, the effect of Tat was maximum at concentrations within the range detected in the sera of HIV-1-infected patients. Anti-Tat antibodies inhibited both effects. Ion secretion and the antiproliferative effects were mediated by L-type Ca(2+) channels. An increase in intracellular calcium concentration in Caco-2 cells was found after addition of Tat.


CONCLUSIONS
These results indicate that Tat may be involved in HIV-1-related intestinal disease through direct interaction with enterocytes.
Canani
Roberto Berni
RB
Department of Pediatrics, University of Naples Federico II, Italy.
Cirillo
Pia
P
Mallardo
Giuseppe
G
Buccigrossi
Vittoria
V
Secondo
Agnese
A
Annunziato
Lucio
L
Bruzzese
Eugenia
E
Albano
Fabio
F
Selvaggi
Francesco
F
Guarino
Alfredo
A
D000328:Adult; D018938:Caco-2 Cells; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D017097:Electric Impedance; D020895:Enterocytes / Q000166:cytology; D015696:Gene Products, tat / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D007425:Intracellular Membranes / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration
D015696:Gene Products, tat; D002118:Calcium