PAK1 is a breast cancer oncogene that coordinately activates MAPK and MET signaling

Abstract

Activating mutations in the RAS family or BRAF frequently occur in many types of human cancers but are rarely detected in breast tumors. However, activation of the RAS-RAF-MEK-ERK Mitogen-Activated Protein Kinase (MAPK) pathway is commonly observed in human breast cancers, suggesting that other genetic alterations lead to activation of this signaling pathway. To identify breast cancer oncogenes that activate the MAPK pathway, we screened a library of human kinases for their ability to induce anchorage-independent growth in a derivative of immortalized human mammary epithelial cells (HMLE). We identified PAK1 as a kinase that permitted HMLE cells to form anchorage-independent colonies. PAK1 is amplified in several human cancer types, including 33% of breast tumor samples and cancer cell lines. The kinase activity of PAK1 is necessary for PAK1-induced transformation. Moreover, we show that PAK1 simultaneously activates MAPK and MET signaling; the latter via inhibition of Merlin. Disruption of these activities inhibits PAK1-driven anchorage-independent growth. These observations establish PAK1 amplification as an alternative mechanism for MAPK activation in human breast cancer and credential PAK1 as a breast cancer oncogene that coordinately regulates multiple signaling pathways, the cooperation of which leads to malignant transformation.

In vivo multiplexed interrogation of amplified genes identifies GAB2 as an ovarian cancer oncogene

“…GAB2 resides on the fourth most significant amplicon in high-grade serous ovarian cancer (3), the focal peak located on 11q14.1. This amplified region has been identified as a recurrent alteration in breast (9,22) and ovarian cancer (19) as well as in metastatic melanoma (24). Across over 6,300 different TCGA samples, this region is among the 26 most amplified regions in all cancers (21).…”

“…GAB2 is required for BCR/ABL-mediated transformation in chronic myeloid leukemia (CML) (31) and also HER2-mediated mammary carcinogenesis through ERK activation (16). Moreover, GAB2 is overexpressed in breast cancer (9,22) and some metastatic melanomas (24) and promotes survival in breast cancer (22) and migration in both malignancies (17,24). Several ovarian cancer cell lines also overexpress GAB2, which was linked to increased migration and the epithelial-mesenchymal transition (26).…”

“…Across 846 samples within the TCGA breast cancer dataset, GAB2 is amplified in 24.7% of samples in which 15% harbor a focal amplification and 8.4% harbor a high-level amplification (21). This region of amplification is slightly larger than in ovarian cancer and also includes PAK1 (9). There are also a small number of lung cancers and glioblastoma that harbor GAB2 amplification.…”

“…We used this experimental model to identify IKBKE and PAK1 as breast cancer oncogenes (8,9). Here we introduced each of the 587 ORFs into HA1E-M cells by transducing each ORF separately in arrayed format.…”

“…In other cancer types, both genome-wide and targeted loss-of-function studies were used to identify novel tumor suppressors in hepatocellular carcinoma (6) and epigenetic regulators in lymphomas (7). In addition, gain-offunction, cDNA-based approaches have uncovered novel driver roles for IKBKE (8) and PAK1 (9) in breast cancer, ERBB3 in endometrial cancer (10), and FGF19 in hepatocellular cancer (11). These studies demonstrate the utility of integrating evidence from both structural and functional assays to identify genes that represent tractable therapeutic targets.…”