Expression of transketolase TKTL1 predicts colon and urothelial cancer patient survival: Warburg effect reinterpreted

Abstract

Tumours ferment glucose to lactate even in the presence of oxygen (aerobic glycolysis; Warburg effect). The pentose phosphate pathway (PPP) allows glucose conversion to ribose for nucleic acid synthesis and glucose degradation to lactate. The nonoxidative part of the PPP is controlled by transketolase enzyme reactions. We have detected upregulation of a mutated transketolase transcript (TKTL1) in human malignancies, whereas transketolase (TKT) and transketolase-like-2 (TKTL2) transcripts were not upregulated. Strong TKTL1 protein expression was correlated to invasive colon and urothelial tumours and to poor patients outcome. TKTL1 encodes a transketolase with unusual enzymatic properties, which are likely to be caused by the internal deletion of conserved residues. We propose that TKTL1 upregulation in tumours leads to enhanced, oxygen-independent glucose usage and a lactate-based matrix degradation. As inhibition of transketolase enzyme reactions suppresses tumour growth and metastasis, TKTL1 could be the relevant target for novel anti-transketolase cancer therapies. We suggest an individualised cancer therapy based on the determination of metabolic changes in tumours that might enable the targeted inhibition of invasion and metastasis.

Figure 1

(A) Quantification of TKTL1 transcripts in gastric carcinoma and lung adenocarcinoma samples, and their corresponding normal tissues. In total, 15 μl of the real-time PCR reaction was loaded onto a 3%-agarose gel to visualise the 150 bp TKTL1 amplification product. Expression differences between tumour and corresponding normal tissue were calculated, and are shown as fold induction in tumour sample relative to the corresponding normal sample. (B) TKTL1 protein expression in tumour and corresponding normal sample of a gastric carcinoma patient with a tumour-specific overexpression of TKTL1 on the transcript level was evaluated by Western blot with antibody JFC12T10. An overexpression of TKTL1 protein was observed in the tumour sample (T) compared to its corresponding normal tissue (N). Sizes of the protein marker are indicated in kDa.

Figure 2

Expression of TKTL1 in normal and carcinoma tissues. Specimens of a gastric carcinoma (C–G) and corresponding normal tissue (A, B); (A, B) no expression of TKTL1 in normal tissue. (C–G) Strong cytoplasmic expression in tumour tissue, but no expression in the surrounding stroma cells. Note the elevated expression within the inner region of the tumour (F). (H, I) Nuclear TKTL1 expression in a poorly differentiated gastric carcinoma. (J) No expression of TKTL1 in a superficial, Ta bladder carcinoma. (K, L) Strong TKTL1 cytoplasmic expression in an invasive, poorly differentiated bladder carcinoma. Strong TKTL1 upregulation in carcinomas of the lung (non-small-cell lung carcinomas; M), breast (N), thyroid (follicular thyroid carcinoma (O), papillary thyroid carcinoma (P)), prostate (Q), and pancreas (R). No expression of TKTL1 in a noninvasive colon carcinoma (S), and strong expression in an invasive colon carcinoma (T). Anti-TKTL1 was revealed by diaminobenzidine tetrahydrochloride (DAB; brown staining) (A–L) and 3-amino-9-ethylcarbazole (AEC; red staining) (M–T).

Figure 3

Upregulation of phosphorylated Akt (p-AKT) in epithelial tumours. Immunohistochemical analysis of p-AKT on paraffin-embedded sections from normal colon as negative control (A), colon cancer (B), papillary (PTC) (C), follicular (FTC) (D), undifferentiated thyroid carcinoma (UTC) (E), non-small-cell lung cancer (NSCLC) (F), bladder cancer (G), and prostate cancer (H) (red staining). All the different types of cancer examined showed strong staining for p-Akt (cytoplasmic, nuclear, or both cytoplasmic and nuclear) while normal tissues showed no or very weak staining (A). A mainly nuclear localisation of p-Akt was been detected in colon, lung, and prostate carcinomas (B, F, H; yellow arrowheads). In all the histological variants of thyroid and bladder cancers, strong cytoplasmic staining was detectable (C–E, G) and only few nuclei in PTC and FTC samples were positive for p-Akt (C, D; yellow arrowheads).

Figure 4

Kaplan–Meier plots demonstrating the significant correlation between TKTL1 staining intensity and survival in colon carcinoma (A), and in urothelial carcinoma (B). Scores indicate the fraction of tumour cells in each sample that stained for TKTL1 protein, as defined in the ‘Materials and methods’ section.