Roberto Rangela, Song-Choon Leeb, Kenneth Hon-Kim Banb,c, Liliana Guzman-Rojasa, Michael B. Manna,
Justin Y. Newberga, Takahiro Kodamaa, Leslie A. McNoed, Luxmanan Selvanesand, Jerrold M. Wardb,1, Alistair G. Ruste,2,
Kuan-Yew Chinb, Michael A. Blackd, Nancy A. Jenkinsa.b.3, and Neal G. Copelanda.b.3.4
a Cancer Research Program, Houston Methodist Research Institute, Houston, TX 77030
b Division of Genomics and Genetics, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Biopolis, Singapore 138673
c Deparment of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 138673
d Department of Biochemistry, University of Otago, Dunedin 9016, New Zealand.
e Experimental Cancer Genetics, Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1HH,
Published online in PNAS before print on November 14, 2016.
Triple-negative breast cancer (TNBC) has the worst prognosis of
any breast cancer subtype. To better understand the genetic forces
driving TNBC, we performed a transposon mutagenesis screen in a
phosphatase and tensin homolog (Pten) mutant mice and identified
12 candidate trunk drivers and a much larger number of
progression genes. Validation studies identified eight TNBC tumor
suppressor genes, including the GATA-like transcriptional repressor
TRPS1. Down-regulation of TRPS1 in TNBC cells promoted
epithelial-to-mesenchymal transition (EMT) by deregulating multiple
EMT pathway genes, in addition to increasing the expression of
SERPINE1 and SERPINB2 and the subsequent migration, invasion,
and metastasis of tumor cells. Transposon mutagenesis has thus
provided a better understanding of the genetic forces driving TNBC
and discovered genes with potential clinical importance in TNBC.
Figure Legend: SB mutagenesis promotes the development
of multiple mammary tumor subtypes. (A) Kaplan–Meier survival curves of five different genotypic
combinations of mice. Pten/SB–Onc2 and Pten/SB–Onc3 mice showed significant tumor acceleration compared with various control mice (Pten/SB–Onc2, P = 0.0003; Pten/SB–Onc3, P = 0.0001). (B and C) H&E or immunohistochemical staining of mammary adenocarcinoma (B) or adenosquamous carcinoma (C). The adenocarcinoma shows areas of less differentiation (Upper H&E). The adenosquamous carcinoma also has areas of no squamous differentiation invading muscle (Lower H&E). Both tumors showed a high degree of heterogeneity, expressing both basal (CK14) and luminal (CK18) cytokeratins. Both tumors have low or focal high-proliferation rate tumors, based upon their Ki67 staining (NOTE-B shows a focally high rate), and express high levels of nuclear SBT protein. (Scale bar, 100 μm.) (D) Mammary tumor subtype classification based upon its PAM50 expression signature (31). The heat map displays gene expression
data (log scale, right legend) for the PAM50 breast cancer subtype classifier for each mouse tumor
(columns). The left side indicates the centroids for each breast cancer subtype. The rows in the heat map represent genes in the PAM50 panel, and columns represent each mammary tumor. Top panels show
proliferation scores (blue, low; red, high) and PAM50 subtypes: basal-like (black), Her2 (purple), luminal A (light blue), and normal-like (light green).