Reserpine-induced alterations in mucus production and calmodulin-binding proteins in a human epithelial cell line

The T84 human colonic adenocarcinoma cell line produces mucin in culture and releases it in response to various secretagogues

The T84 colonic adenocarcinoma cell line, which has been used extensively as a model for studies of epithelial chloride secretion, also produces mucin and secretes it in culture. Electron microscopy of fixed sections of cultured cells, along with Immunogold labelling with an antibody to human small intestine (SI) mucin, revealed the presence of goblet-like cells with mucin-containing secretory granules. The mucin was of high molecular mass, had an amino acid composition similar to that of purified human SI and colonic mucins, and competed effectively with SI mucin for binding to the anti-(SI mucin) antibody. A sensitive solid-phase immunoassay specific for intestinal mucins was developed and used to measure mucin secretion by T84 cells. Cultures were treated for 30 min at 37 degrees C with a number of agents known to cause chloride secretion by T84 cell monolayers and the amount of mucin appearing in the medium was measured. Carbachol (1 mM), A23187 (10 microM), prostaglandin E1 (PGE1) (1 microM) and vasoactive intestinal polypeptide (VIP) (0.1 microM) all stimulated mucin release, but histamine (1 mM) had no effect. Whereas VIP is reported to stimulate chloride secretion more strongly than carbachol, it was less effective than carbachol in stimulating mucin secretion. Phorbol 12-myristate 13-acetate (PMA) (0.1-10 microM) also stimulated mucin release strongly, implicating a responsive protein-kinase C-dependent pathway. Additive secretory responses were obtained with combined stimulation by VIP (10 nM-1 microM) and carbachol (1 mM). Responses to stimulation with A23187 (1-10 microM) together with PMA (10 nM-10 microM) suggest that cytosolic Ca2+ concentration is a modulator of PMA activity.

Identification of a 52-kD calmodulin-binding protein associated with the mitotic spindle apparatus in mammalian cells

A pool of 10 calmodulin-binding proteins (CBPs) was isolated from Chinese hamster ovary (CHO) cells via calmodulin (CaM)-Sepharose affinity chromatography. One of these ten isolated CBPs with a molecular mass of 52 kD was also found to be present in isolated CHO cell mitotic spindles. Affinity-purified antibodies generated against this pool of isolated CBPs recognize a single 52-kD protein in isolated CHO cell mitotic spindles by immunoblot analysis. Immunofluorescence examination of CHO, 3T3, NRK, PTK-2, and HeLa cells resulted in a distinct pattern of mitotic spindle fluorescence. The localization pattern of this 52-kD CBP directly parallels that of CaM in the spindle apparatus throughout the various stages of mitosis. Interestingly, there was no association of this 52-kD CBP with cytoplasmic microtubules. As is the case with CaM, the localization pattern of the 52-kD CBP in interphase cells is diffuse within the cytoplasm and is not associated with any discrete, cellular structures. This 52-kD CBP appears to represent the first mitotic spindle-specific calmodulin-binding protein identified and represents an initial step toward the ultimate determination of CaM function in the mitotic spindle apparatus.