Deletion and Overexpression of the Scaffolding Protein IQGAP1 Promotes Hepatocellular Carcinoma
Authors: Delgado Evan R. , Erickson Hanna , Tao Junyan , Leek Madeleine , Monga Satdarshan , Duncan Andrew 
Published: April 2020

Background

Hepatocellular Carcinoma (HCC) is the 5th most common cause of cancer‐related death with an estimated 32,000 annual deaths in the United States. Current treatment methods provide minimal results and can be improved by a more concrete understanding of the underlying mechanisms driving the disease.

Sixty‐85% of HCCs are characterized by elevated IQGAP1 protein expression. IQGAP1 is a scaffold protein that binds signaling molecules associated with cellular proliferation to regulate or enhance their activity. While overexpression of IQGAP1 is associated with HCC, other studies indicate IQGAP1 loss enhances tumorigenic signals. Clearly, maintaining IQGAP1 expression is critical for normal tissue homeostasis.

Methods

We asked if IQGAP1 overexpression exacerbates HCC growth. To do this, we used hydrodynamic tail vein injections with the Sleeping Beauty transposase to model HCC. The transposon system can induce HCC in wild‐type, adult mice which are 69% genetically similar to human HCC when human activated (S45Y) □‐catenin and MET (B +M) are expressed in hepatocytes. We included the overexpression of IQGAP1 in this model system and subsequently investigated downstream pro‐growth and survival mechanisms that are regulated by IQGAP1.

Additionally, studies suggest that IQGAP1 loss promotes oncogenic signaling. Therefore, we asked if IQGAP1 loss will impact HCC tumorigenesis. Here, we used the diethylnitrosamine (DEN) chemical carcinogenesis model to induce HCC in mice lacking Iqgap1 expression. Following tumorigenesis, we again investigated mechanisms that may become dysregulated upon loss of IQGAP1 expression.

Results

After 8.5 weeks, overexpression of B+M with IQGAP1 (B+M+I) in the transposon system resulted in 2‐fold higher LW/BW ratio compared to B+M – indicating potential increased tumor burden. Alpha‐fetoprotein, a marker of highly aggressive HCC, was highest in the B+M+I group. Several canonical Wnt target genes (e.g., Bric5, Lect2, and Glul) were elevated in the B+M+I group. Additionally, we measured increased nuclear □‐catenin in B+M+I compared to B+M tissues after 4 weeks in the transposon model. To test if IQGAP1 overexpression enhances Wnt/□‐catenin activity, we overexpressed IQGAP1 in vitro and found increased nuclear □‐catenin in addition to elevated Wnt/□‐catenin reporter activity.

Analysis of Iqgap1−/− tissues after DEN resulted in increased HCC tumor burden compared to control mice. Tumors in Iqgap1−/− mice demonstrated increased proliferation verified by Ki‐67 staining. Finally, we found that loss of Iqgap1 causes elevated MET expression and activation leading to HCC, and can be targeted in vitro by using the MET small molecule inhibitor, EMD‐1214063.

Conclusion

Together, our data suggests that dysregulation of IQGAP1 expression drives HCC in our models. Elevated IQGAP1 enhances □‐catenin signaling while IQGAP1 loss causes higher MET expression and activity. Our data indicate that IQGAP1 is in a delicate balance in the liver and any changes can result in HCC oncogenesis.

Support or Funding Information

This work supported by the NIH to AWD (R01DK103645).

Summary of IQGAP1 mechanism in Hepatocellular Carcinoma

Figure 1