Expression of the stress response oncoprotein LEDGF/p75 in human cancer: a study of 21 tumor types

Abstract

Oxidative stress-modulated signaling pathways have been implicated in carcinogenesis and therapy resistance. The lens epithelium derived growth factor p75 (LEDGF/p75) is a transcription co-activator that promotes resistance to stress-induced cell death. This protein has been implicated in inflammatory and autoimmune conditions, HIV-AIDS, and cancer. Although LEDGF/p75 is emerging as a stress survival oncoprotein, there is scarce information on its expression in human tumors. The present study was performed to evaluate its expression in a comprehensive panel of human cancers. Transcript expression was examined in the Oncomine cancer gene microarray database and in a TissueScan Cancer Survey Panel quantitative polymerase chain reaction (Q-PCR) array. Protein expression was assessed by immunohistochemistry (IHC) in cancer tissue microarrays (TMAs) containing 1735 tissues representing single or replicate cores from 1220 individual cases (985 tumor and 235 normal tissues). A total of 21 major cancer types were analyzed. Analysis of LEDGF/p75 transcript expression in Oncomine datasets revealed significant upregulation (tumor vs. normal) in 15 out of 17 tumor types. The TissueScan Cancer Q-PCR array revealed significantly elevated LEDGF/p75 transcript expression in prostate, colon, thyroid, and breast cancers. IHC analysis of TMAs revealed significant increased levels of LEDGF/p75 protein in prostate, colon, thyroid, liver and uterine tumors, relative to corresponding normal tissues. Elevated transcript or protein expression of LEDGF/p75 was observed in several tumor types. These results further establish LEDGF/p75 as a cancer-related protein, and provide a rationale for ongoing studies aimed at understanding the clinical significance of its expression in specific human cancers.

Figure 1. Transcript expression of LEDGF/p75 in eight human cancer types determined by TissueScan Cancer Q-PCR analysis.

Data were analyzed using the ΔΔCt method with values normalized to β-actin levels. The y-axis represents the induction fold of the LEDGF/p75 mRNA level in eight cancer types (n = 9) compared to matching normal adjacent tissues (n = 3) in the array. Error bars displays the range of standard error. * P<0.05. P values were determined with Student's t-test.

Figure 2. Identification of LEDGF/p75 specific antibody by immunoblotting in PC-3 cells with transient LEDGF/p75 knockdown.

Cells were transfected with siLEDGF/p75 to induce transient knockdown of LEDGF/p75. PC-3 cells transfected with small interfering scrambled RNA duplex (siSD) served as corresponding control. Immunoblotting analysis tested the specific reactivity of all the antibodies against LEDGF/PSIP1. All the blot pairs (siSD and siLEDGF/p75) for each antibody were derived from the same blot.

Figure 3. Elevated immunohistochemical expression of LEDGF/p75 protein in five tumor types compared to corresponding normal tissues.

Tissue microarrays were stained with antibody against LEDGF/p75, and the individual cores were blindly scored using the following scale: 0 = no staining, 1 = low staining, 2 = moderate staining, 3 = strong staining. Scored tissues were pooled into two groups: low staining (scores 0 and 1, dark bars) and high staining (scores 2 and 3, light bars). The percentage of specimens in the two staining categories was plotted for tumor tissues compared to normal (including disease-free normal and normal adjacent) tissues. *P<0.05; **P<0.01. P values were determined with Fisher's exact test.

Figure 4. Immunohistochemical staining for LEDGF/p75 protein in selected human tumors.

A. Representative images of immunohistochemical staining (low intensity, scores 0–1; high intensity, scores 2–3) for LEDGF/p75 in prostate, colon, and thyroid tumors (Scale bar-40 µm; magnification = 200×). B. Representative images of LEDGF/p75 immunostaining of non-disease normal prostate and colon tissues, and in tumor tissues and their matched adjacent tissues (Scale bar-40 µm; magnification = 400×). TMAs were stained using LEDGF/p75 specific rabbit antibody Scripps-Ab5087, as indicated in Materials and Methods. Identical camera settings were used in the acquisition and processing of images for a particular tissue type.