Increased Tight Junction Permeability Can Result from Protein Kinase C Activation/Translocation and Act as a Tumor Promotional Event in Epithelial Cancers

Abstract

Exposure of LLC‐PK1 epithelial cell cultures to phorbol ester tumor promoters causes immediate translocation of protein kinase C‐α (PKC‐α) from cytosolic to membrane‐associated compartments. With a very similar time course, a dramatic and sustained increase in tight junctional (paracellular) permeability occurs. This increased permeability extends not only to salts and sugars but macromolecules as well. Fortyfold increases of transepithelial fluxes of biologically active EGF and insulin occur. Recovery of tight junction barrier function coincides with proteasomal downregulation of PKC‐α. The failure to downregulate activated membrane‐associated PKC‐α has correlated with the appearance of multilayered cell growth and persistent leakiness of tight junctions. Accelerated downregulation of PKC‐α results in only a partial and transient increase in tight junction permeability. Transfection of a dominant/ negative PKC‐α results in a slower increase in tight junction permeability in response to phorbol esters. In a separate study using rat colon, dimethylhydrazine (DMH)‐induced colon carcinogenesis has been preceded by linear increases in both the number of aberrant crypts and transepithelial permeability, as a function of weeks of DMH treatment. Adenocarcinomas of both rat and human colon have been found to have uniformly leaky tight junctions. Whereas most human colon hyperplastic and adenomatous polyps contain nonleaky tight junctions, adenomatous polyps with dysplastic changes did possess leaky tight junctions. Our overall hypothesis is that tight junctional leakiness is a late event in epithelial carcinogenesis but will allow for growth factors in luminal fluid compartments to enter the intercellular and interstitial fluid spaces for the first time, binding to receptors that are located on only the basal‐lateral cell surface, and causing changes in epithelial cell kinetics. Tight junctional leakiness is therefore a promotional event that would be unique to epithelial cancers.

Phosphorylation of claudin-4 by PKCε regulates tight junction barrier function in ovarian cancer cells

“…Our results suggest that PKCε's role in metastasis may be related to its ability to impair the barrier function (and cell adhesion) through phosphorylation of TJ proteins such as claudin-4. These findings are consistent with a number of studies that have previously shown that phosphorylation of various claudin proteins can decrease TJ integrity [32,35,[51][52][53][54], although phosphorylation of claudin-1 has also been shown to promote barrier function [29,31]. However, it is important to note that TJ disruption likely occurs through multiple mechanisms.…”

The Role of Protein Kinase C Isoforms in Modulating Injury and Repair of the Intestinal Barrier

“…PKC isoforms in the gastrointestinal tract are involved in several vital intracellular pathways, including cell proliferation/cytostasis (Batlle et al, 1998;Verstovsek et al, 1998;Assert et al, 1999;Umar et al, 2000), cell differentiation (Abraham et al, 1998;Verstovsek et al, 1998;Frey et al, 2001), apoptosis (Chang and Tepperman, 2001;Frey et al, 2001), cell adhesion (Batlle et al, 1998;Hollande et al, 2003), membrane remodeling (Song et al, 1999(Song et al, , 2002, epithelial migration (Andre et al, 1999), transepithelial permeability (Marano et al, 2001), ion secretion (Van den Berghe et al, 1992;Yoo et al, 2001), receptor and brush border enzyme expression (Murray et al, 2002), cytoskeletal modulation (Fasano et al, 1995;Banan et al, 2002aBanan et al, ,c,d, 2003aBanan et al, ,b, 2004a, tight junction modification , and epithelial responses to inflammatory Tepperman, 2001, 2003), cytotoxic Chang and Tepperman, 2001), and carcinogenic (Pongracz et al, 1995;Murray et al, 1999Murray et al, , 2002Perletti et al, 1999;Mullin et al, 2000) mediators. These multiple roles suggest that this group of enzymes is involved in the regulation of the health and damage of epithelial cells and the intestinal barrier.…”

“…PKC-␣ has been associated with several cell functions. Mullin et al (2000) and showed that phorbol ester tumor promoters, which are general PKC activators, cause immediate translocation of PKC-␣ from cytosolic-to membrane-associated compartments. This translocation is associated with paracellular leakiness and multilayered cell growth.…”

Styrene maleic acid-encapsulated paclitaxel micelles: antitumor activity and toxicity studies following oral administration in a murine orthotopic colon cancer model

“…5,6 Thus, oral administration would be an efficient strategy for treatment of colorectal cancer, since the chemotherapeutic agent could effectively reach the tumor site. However, oral administration of PTX is associated with a number of limitations.…”

“…sMa paclitaxel micelles for oral delivery the intestinal epithelium due to tight junction modifications, 5,6 SMA-PTX micelles can pass paracellularly due to the modified tight junctions and reach the tumor site beneath the epithelium. Thus, together these pathways could contribute to the enhanced uptake of SMA-PTX micelles by the colon tumors, resulting in a greater therapeutic effect.…”