Changes in P-glycoprotein expression in gastric carcinoma with respect to distant gastric mucosa may be influenced by p53

P-glycoprotein: new insights into structure, physiological function, regulation and alterations in disease

The multidrug resistance phenomenon presents a major threat to the pharmaceutical industry. This resistance is a common occurrence in several diseases and is mediated by multidrug transporters that actively pump substances out of the cell and away from their target regions. The most well-known multidrug transporter is the P-glycoprotein transporter. The binding sites within P-glycoprotein can accommodate a variety of compounds with diverse structures. Hence, numerous drugs are P-glycoprotein substrates, with new ones being identified every day. For many years, the mechanisms of action of P-glycoprotein have been shrouded in mystery, and scientists have only recently been able to elucidate certain structural and functional aspects of this protein. Although P-glycoprotein is highly implicated in multidrug resistant diseases, this transporter also performs various physiological roles in the human body and is expressed in several tissues, including the brain, kidneys, liver, gastrointestinal tract, testis, and placenta. The expression levels of P-glycoprotein are regulated by different enzymes, inflammatory mediators and transcription factors; alterations in which can result in the generation of a disease phenotype. This review details the discovery, the recently proposed structure and the regulatory functions of P-glycoprotein, as well as the crucial role it plays in health and disease.

Relevance of P-glycoprotein on CXCR4+ B cells to organ manifestation in highly active rheumatoid arthritis

INTRODUCTION

In rheumatoid arthritis (RA), P-glycoprotein (P-gp) expression on activated B cells is associated with active efflux of intracellular drugs, resulting in drug resistance. CXCR4 is associated with migration of B cells. This study was designed to elucidate the relevance of P-gp expression on CXCR4⁺ B cells to clinical manifestations in refractory RA.

METHODS

CD19⁺ B cells were analyzed using flow cytometry and immunohistochemistry.

RESULTS

P-gp was highly expressed especially on CXCR4⁺CD19⁺ B cells in RA. The proportion of P-gp-expressing CXCR4⁺ B cells correlated with disease activity, estimated by Simplified Disease Activity Index (SDAI), and showed marked expansion in RA patients with high SDAI and extra-articular involvement. In highly active RA, massive infiltration of P-gp⁺CXCR4⁺CD19⁺ B cells was noted in CXCL12-expressing inflammatory lesions of RA synovitis and RA-associated interstitial pneumonitis. In RA patient with active extra-articular involvement, intracellular dexamethasone level (IDL) in lymphocytes diminished with expansion of P-gp⁺CXCR4⁺ CD19⁺ B cells. Adalimumab reduced P-gp⁺CXCR4⁺ CD19⁺ B cells, increased IDL in lymphocytes, and improved the clinical manifestation and allowed tapering of concomitant medications.

CONCLUSIONS

Expansion of P-gp⁺CXCR4⁺ B cells seems to be associated with drug resistance, disease activity and progressive destructive arthritis with extra-articular involvement in RA.

Association between ABCB1 immunohistochemical expression and overall survival in gastric cancer patients

Gastric cancer (GC) is one of the most common malignancies worldwide. The ABCB1 protein, a member of the ATP-binding cassette (ABC) transporter family, encoded by the ABCB1 gene, considerably influences the distribution of drugs across cell membranes as well as multidrug resistance (MDR) of antineoplastic drugs. In contrast to the extensive knowledge on the pharmacological action of ABCB1 protein, the correlation between the clinical-pathological data and ABCB1 protein expression in patients with GC remains unclear. The aim was to investigate association between ABCB1 expression and overall survival in GC patients. Human tumor fragments from 57 GC patients were examined by immunohistochemistry assay. We observed lower survival rate of patients with GC who were positive for ABCB1 expression (p=0.030). Based on these observations, we conclude that GC patients with positive ABCB1 protein immunohistochemical expression in their tumors suffer shorter overall survival.

Multidrug resistance-associated protein (MRP1) gene is strongly expressed in gastric carcinomas. Analysis by immunohistochemistry and real-time quantitative RT-PCR

AIMS

To assess MRP1 protein and MRP1 mRNA levels in gastric carcinomas and in non-neoplastic mucosa remote from the tumours. MRP1 gene expression may play a role in the complex pattern of chemoresistance present in gastric carcinomas.

METHODS AND RESULTS

A total of 57 carcinomas and respective gastric tissues were included for immunohistochemical assessment with the anti-MRP1 monoclonal antibodies MRPr1 and QCRL-1. Of these, 35 tumour and gastric mucosa tissues were also assessed by real-time quantitative reverse transcriptase-polymerase chain reaction. Medium or high MRP1 protein expression was detected in 89% and 77% of carcinomas and in 96% and 93% of non-neoplastic gastric mucosa by MRPr1and QCRL-1, respectively. No difference in MRP1 mRNA levels was detected between carcinomas and non-neoplastic gastric mucosa tissues in 77% of the patients. A significant correlation was found between MRP1 mRNA level and protein expression detected in carcinomas related to non-neoplastic gastric mucosa, although they were non-concordant in 29% of the patients.

CONCLUSIONS

MRP1 gene is usually expressed in most gastric carcinomas and does not differ substantially from that observed in non-neoplastic gastric mucosa remote from the tumour. However, a decrease in MRP1 gene expression is found in some carcinomas. For accurate assessment of changes in MRP1 expression between tumour and normal tissues both protein and mRNA detection are necessary.

ATP-binding cassette superfamily transporter gene expression in human soft tissue sarcomas

The phenomenon of multidrug resistance (MDR) in various malignant neoplasms has been reported as being caused by one or multiple expressions of ATP-binding cassette (ABC) superfamily protein, including P-glycoprotein/multidrug resistance (MDR) 1 and the MDR protein (MRP) family. However, their expression levels and distribution within soft tissue sarcomas remain controversial. In 86 cases of surgically resected soft tissue sarcoma, intrinsic mRNA levels of MDR1, MRP1, MRP2 and MRP3 were assessed using a quantitative reverse transcriptase-PCR (RT-PCR) method. Moreover, immunohistochemical protein expressions of P-glycoprotein (P-gp), MRP1, MRP2, MRP3 and p53 protein were evaluated in concordant paraffin-embedded material. The mRNA expression and immunohistochemical expression of ABC superfamily transporters were compared to clinicopathologic parameters and proliferative activities as evaluated by the MIB-1-labeling index (LI). Among the various histologic types, malignant peripheral nerve sheath tumor (MPNST) showed significantly high levels of MDR1 (p=0.017) and MRP3 (p=0.0384) mRNA expression, compared to the other tumor types. When the immunohistochemical method was compared to the RT-PCR technique to assess ABC transported expression at the protein and mRNA levels, a significantly close relationship was found between the 2 methods (p<0.05). P-gp expression was significantly correlated with large tumor size (> or =5 cm, p=0.041) and high AJCC stage (stages III and IV) (p=0.0365). Furthermore, cases with nuclear expression of p53 revealed significantly higher levels of MDR1 mRNA expression, compared to those with negative immunoreaction for p53 (p=0.0328). Our results suggest that MDR1/P-gp expression may have an important role to play in tumor progression in the cases of soft tissue sarcoma, and p53 may be one of the active regulators of the MDR1 transcript. In addition, the high levels of both MDR1 and MRP3 mRNA expression in MPNST may help to explain the poor response of this tumor to anticancer-drugs.

Clinicopathological significance and survival influence of p53 protein expression in gastric carcinoma

AIMS

Mutations in the gene coding for p53 protein are among the most frequent genetic alterations observed in human cancers. The relevance and biological significance of p53 expression in gastric carcinoma are far from being fully established. The aim of our study was to evaluate the influence of p53 detected by immunohistochemistry in the clinicopathological behaviour of a series of gastric carcinoma cases.

METHODS AND RESULTS

Samples from 163 patients treated by gastric resection for gastric carcinoma between 1988 and 1995 were used. Surgical specimens were evaluated for the presence of p53 protein detected by immunohistochemistry with a monoclonal antibody. Cases were classified as positive or negative for p53. Several clinicopathological parameters and c-erb B-2 expression were analysed in the same series and compared with the expression of p53. Cumulative survival was evaluated using univariate analysis and Cox model regression. p53 expression was identified in 41 carcinomas (25.2%) and was significantly associated with venous invasion (P = 0.049), lymph node metastases (P = 0.01) and c-erb B-2 expression (P = 0.003). All the parameters except gender, tumour size and Laurén's classification influenced survival on univariate analysis. p53 expression correlated with overall survival (P = 0.006) and survival in the subgroup of patients with intestinal type carcinoma (P = 0.04). In the subgroup of patients with carcinomas not expressing c-erb B-2, p53 expression significantly influenced cumulative survival (P = 0.02).

CONCLUSIONS

p53 expression is associated with the aggressive biological behaviour of gastric carcinomas and is related to cumulative survival.