Thioredoxin Interacting Protein (TXNIP) Is Differentially Expressed in Human Tumor Samples but Is Absent in Human Tumor Cell Line Xenografts: Implications for Its Use as an Immunosurveillance Marker

Abstract

Thioredoxin interacting protein (TXNIP) is a metabolic protein critically involved in redox homeostasis and has been proposed as a tumor suppressor gene in a variety of malignancies. Accordingly, TXNIP is downregulated in breast, bladder, and gastric cancer and in tumor transplant models TXNIP overexpression inhibits growth and metastasis. As TXNIP protein expression has only been investigated in few malignancies, we employed immunohistochemical detection in a large multi-tumor tissue microarray consisting of 2,824 samples from 94 different tumor entities. In general, TXNIP protein was present only in a small proportion of primary tumor samples and in these cases was differently expressed depending on tumor stage and subtype (e.g., renal cell carcinoma, thyroid cancer, breast cancer, and ductal pancreatic cancer). Further, TXNIP protein expression was determined in primary mouse xenograft tumors derived from human cancer cell lines and was immunohistochemically absent in all xenograft tumors investigated. Intriguingly, TXNIP expression became gradually lower in the proximity of the primary tumor tissue and was absent in leukocytes directly adjacent to tumor tissue. In conclusion, these findings suggest that TXNIP downregulation is as a common feature in human tumor xenograft models and that intra-tumoral leukocytes down-regulate TXNIP. Hence TXNIP expression might be used to monitor the functional state of tumor-infiltrating leukocytes in tissue sections.

Keywords: cancer; immunotherapy; reactive oxygen species; thioredoxin; thioredoxin interacting protein; tissue array; tumorigenesis; xenograft.

Figure 1

Representative images of thioredoxin interacting protein (TXNIP) immunostaining results on multi-tumor tissue micro array (TMA). (a) Strong TXNIP protein expression in an oncocytoma sample, (b) moderate TXNIP protein expression in a hepatocellular carcinoma sample, (c) weak TXNIP protein expression in a mucinous ovarian cancer sample, (d) negative TXNIP protein expression in an anaplastic thyroid cancer sample. Staining with Permanent Red. Scale bar (upper panel) = 100 µm, scale bar (lower panel) = 50 µm.

Figure 2

Differential expression of thioredoxin interacting protein (TXNIP) in selected tumor types and subtypes on multi-tumor TMA. (a) Thyroid cancer subtypes, (b) breast cancer subtypes, (c) lung cancer including non-small cell lung cancer (NSCLC) subtypes and small-cell lung cancer (SCLC), (d) renal cell cancer, (e) urothelial cancer (pTa = non-invasive papillary carcinoma, pT2-4 = invasive carcinoma), and (f) colo-rectal cancer (CRC). ‘−‘ = negative, ‘+’ = weak, ‘++’ = moderate, and ‘+++’ = strong TXNIP expression.

Figure 3

Percentage of thioredoxin interacting protein (TXNIP)-positive tumor samples of all tumor samples in adenocarcinomas (a) and squamous cell carcinomas (b) on multi-tumor TMA. ‘+’ = high, ‘−‘ = low TXNIP protein expression. NSCLC = Non-small cell lung cancer.

Figure 4

Thioredoxin interacting protein (TXNIP) and CD45 immunostaining results in a HT-29 mouse xenograft tumor. Scale bar (upper panel) = 500 µm, scale bar (lower panel) = 200 µm.

Figure 5

Thioredoxin interacting protein (TXNIP) and CD45 immunostaining results in mouse xenograft tumors derived from different tumor cell lines. Scale bar: LNCaP = 1000 µm, LOX-IMVI = 200 µm, MDA-MB-435 = 200 µm, BxPC-3 = 500 µm, HOS = 200 µm.

Figure 6

Downregulation of thioredoxin interacting protein (TXNIP) in intra- and peri-tumoral leukocytes. Scale bar: LOX-IMVI = 100 µm, PaCa 5072 = 500 µm.