p-21 Activated Kinase as a Molecular Target for Chemoprevention in Diabetes

Abstract

Anti-diabetic drugs modulate p-21 activated kinase (PAK) signaling. Introduction: Type 2 diabetes mellitus (T2DM) is a chronic inflammatory disease associated with increased cancer risk. PAK signaling is implicated in cellular homeostasis when regulated, and cancer when unrestrained. Recent reports provided a role for PAK signaling in glucose homeostasis, but the role of PAKs in the pathogenesis of T2DM is unknown. Here, we performed a mini-meta-analysis to explore if anti-diabetic drugs modify PAK signaling pathways, and provide insight regarding modulation of these pathways, to potentially reduce diabetes-associated cancer risk. Methods: PAK interacting partners in T2DM were identified using the online STRING database. Correlation studies were performed via systematic literature review to understand the effect of anti-diabetic drugs on PAK signaling. A mini-meta-analysis correlated multiple clinical studies and revealed the overall clinical response rate and percentage of adverse events in piogliazone (n = 53) and metformin (n = 91) treated patients with PAK-associated diseases. Results: A total of 30 PAK interacting partners were identified (10: reduced beta-cell mass; 10: beta-cell dysfunction; 10: obesity-insulin resistance), which were highly associated with Wnt, and G-protein signaling. The anti-diabetic drug metformin activated signaling pathways upstream; whereas pioglitazone inhibited pathways downstream of PAK. Overall, clinical response upon pioglitazone treatment was 53%. Seventy-nine percent of pioglitazone and 75% of metformin treated patients had adverse events. Pioglitazone reduced molecular-PAK biomarkers of proliferation (Ki67 and CyclinD1), and metformin had the opposite effect. Conclusions: PAK signaling in T2DM likely involves Wnt and G-protein signaling, which may be altered by the anti-diabetic drugs metformin and pioglitazone. Apart from the therapeutic limitations of adverse events, pioglitazone may be promising in chemoprevention. However long-term multi-centered studies, which initiate pioglitazone treatment early will be required to fully assess the full potential of these drugs.

Keywords: cancer; chemoprevention; inflammation; metformin; p-21 activated kinase; pioglitazone; type 2 diabetes mellitus.

Figure 1

(A–E) PAK interacting partners are associated with pathogenesis of T2DM. PAK interacting partners were identified with STRING database, using known targets involved in (A) reduced beta-cell mass, (B) beta-cell dysfunction, and (C) obesity/insulin resistance. (D) Novel PAK interacting partners involved in reduced beta-cell mass, beta cell dysfunction, and obesity/insulin resistance are displayed and color coded based on their involvement in the cell cycle (blue); G-proteins (green); receptor tyrosine kinase (red); and Wnt signaling (purple). (E) Bar graphs indicate the number of interacting partners involved in pathway associated with pathogenesis of T2DM. Reduced beta cell mass is associated with the cell cycle, beta cell dysfunction is associated with Wnt signaling, and obesity/insulin resistance is associated with receptor tyrosine kinases. G-proteins are associated with all three pathways leading to T2DM.

Figure 2

(A–F) Anti-diabetic drugs utilize upstream and downstream PAK signaling pathways. (A) Pie graph indicates total number of PAK signaling pathways utilized by metformin, glyburide, or glitazone. (B) Total number of pathways utilized by anti-diabetic drugs upstream or downstream of PAK. Note that total number of pathways in (A,B) are not equal as pathways interfered by drug may involve targets both up and downstream PAK. All bar graphs indicate the number of PAK signaling pathways involved in inflammation (C), proliferation (D), survival (E), and angiogenesis (F) upstream or downstream of PAK, which are either activated or inhibited by anti-diabetic drugs. See text for statistics.

Figure 3

(A,B) Pioglitazone and metformin have therapeutic limitation in cancer patients. (A) Pie graphs demonstrate study type, design, and disease associated with their respective treatment. (B) Clinical analyses included calculation of overall response rate and number of serious or other adverse events in pio and met treated patients. Results are pooled data from 53 pio treated patients [NCT00099021 (n = 21), NCT00951379 (n = 26), NCT01342770 (n = 6)] and 91 met treated patients [NCT01433913 (n = 10), NCT01447927 (n = 36), NCT01312467 (n = 45)]. Serious or other adverse events were defined based on ClinicalTrial.gov. See text for statistical analysis.

Figure 4

Pioglitazone and metformin alter biomarkers downstream of PAK in human disease. Bar graphs are data representing expression of biomarkers calculated by IHC in patients treated with (+ or -) pio [NCT00951379 (n = 25), NCT01342770 (n = 5)] or met [NCT01433913 (n = 8), NCT01447927 (n = 36), NCT01312467 (n = 32)]. See text for statistical analysis.

Figure 5

Role of PAK signaling in response to inflammation, altered microbiota and hyperglycemia. Image is read from left to right. (Far left) Binding of a Wnt ligand to the Frizzled receptor disrupts the multi-subunit destruction complex consisting of Axin, Dvl, GSK3beta, and APC, which normally tags Beta-catenin to the proteasome. Here, beta-catenin is no longer degraded but moves to the nucleus where it binds to TCF/LEF and initiates transcription of target genes involved in cell cycle progression, proliferation and survival. (Low left) Ligand binding to PPARγ results in its activation and nuclear translocation where it then binds RXR and induces its own transcription as well as genes involved in glucose homeostasis and lipid transport. PPARγ directly inhibits Beta-catenin and the NF-κB subunit RelA. (Central) Inflammatory cytokines like TNFalpha or microbial products such as EspG or lipopolysaccharides (LPS), result in PAK1 activation. PAK1 phosphorylates Beta-catenin and leads to its stabilization and full transcriptional activation. PAK1 phosphorylates JNK and activates the IKK complex which disrupts RelA from IkB and leading to transcription of genes involved in inflammation and survival. Hyperglycemia results in insulin stimulation of RTKs which further activate PAK1 or directly contribute to a PI3K/AKT/mTOR pathway. PAK1 may also directly contribute to activation of PI3K or mTOR or vice versa. Note that activation of the mTOR1-Raptor complex leads to transcription of PPARγ. As PPARγ levels increase they fulfill their role in the nucleus and cytoplasm. RAS is a key component of the MAPK and PI3K pathway. MAPK-ERK signaling results in activation of JUN and FOS (nucleus) and inhibits PPARγ (cytoplasm). (Far right) RAC1/CDC42 are small Rho-GTPases, which also lead to PAK1 activation. PAK1 stimulates the MAPK-ERK cascade and also inhibits PPARγ.