Knock-in of Mutant K-<i>ras</i> in Nontumorigenic Human Epithelial Cells as a New Model for Studying K-<i>ras</i>–Mediated Transformation

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Recurrent human epidermal growth factor receptor 2 (HER2) missense mutations have been reported in human cancers. These mutations occur primarily in the absence of HER2 gene amplification such that most HER2-mutant tumors are classified as "negative" by FISH or immunohistochemistry assays. It remains unclear whether nonamplified HER2 missense mutations are oncogenic and whether they are targets for HER2-directed therapies that are currently approved for the treatment of HER2 gene-amplified breast cancers. Here we functionally characterize HER2 kinase and extracellular domain mutations through gene editing of the endogenous loci in HER2 nonamplified human breast epithelial cells. In in vitro and in vivo assays, the majority of HER2 missense mutations do not impart detectable oncogenic changes. However, the HER2 V777L mutation increased biochemical pathway activation and, in the context of a PIK3CA mutation, enhanced migratory features in vitro. However, the V777L mutation did not alter in vivo tumorigenicity or sensitivity to HER2-directed therapies in proliferation assays. Our results suggest the oncogenicity and potential targeting of HER2 missense mutations should be considered in the context of cooperating genetic alterations and provide previously unidentified insights into functional analysis of HER2 mutations and strategies to target them. A great success in the treatment of breast cancer has come from the identification of human epidermal growth factor receptor 2 (HER2)/Neu (ERBB2) amplification/overexpression as a targetable driver in ∼20% of breast cancers (1). HER2 is a member of the ErbB family of transmembrane receptor tyrosine kinases, which includes the epidermal growth factor receptor (EGFR/ErbB1), HER3 (ErbB3), and HER4 (ErbB4) (2). Activation of ErbB signaling causes receptor tyrosine autophosphorylation and induces interactions with cytoplasmic signal transduction partners that promote a wide variety of cellular processes including proliferation, motility, and escape from apoptosis. In addition to their key role in normal cellular growth and maintenance, the dysregulation of ErbB receptors has been extensively implicated in the development of numerous cancers (1).Whereas overexpression or amplification of HER2 has been well described to deregulate ErbB signaling, cancer genome sequencing studies have demonstrated that somatic point mutations in the HER2 gene occur in a number of cancers, including 2-4% of breast cancers (3-6). Importantly, these mutations are most often found in patients as single copies without amplification/overexpression of HER2 (HER2-"negative" breast cancers), though HER2 protein expression is often still present. Overexpression studies have implicated a number of these mutations as activating and oncogenic (4, 7-9). Additionally, one mutation, L755S, has been described to be associated with lapatinib resistance when overexpressed (4, 10).Past studies comparing overexpression of a mutant cDNA to single nucleotide knockin of mutant oncogenes have shown dramatic differences ...

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confidence: 64%

“…Cells were washed and seeded in the indicated media. After 48 h, protein lysates were harvested, and immunoblotting was conducted as previously described (11). See SI Materials and Methods for details and a list of primary antibodies.…”

Section: Methodsmentioning

confidence: 99%

HER2 missense mutations have distinct effects on oncogenic signaling and migration

Zabransky

Yankaskas

Cochran

et al. 2015

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“…Cell lines used have been described (31). Overexpression and shRNA constructs used for transfection and assays were performed as described (37,38).…”

Section: Methodsmentioning

confidence: 99%

MACROD2 overexpression mediates estrogen independent growth and tamoxifen resistance in breast cancers

Mohseni

Cidado

Croessmann

et al. 2014

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Tamoxifen is effective for treating estrogen receptor-alpha (ER) positive breast cancers. However, few molecular mediators of tamoxifen resistance have been elucidated. Here we describe a previously unidentified gene, MACROD2 that confers tamoxifen resistance and estrogen independent growth. We found MACROD2 is amplified and overexpressed in metastatic tamoxifen-resistant tumors. Transgene overexpression of MACROD2 in breast cancer cell lines results in tamoxifen resistance, whereas RNAi-mediated gene knock down reverses this phenotype. MACROD2 overexpression also leads to estrogen independent growth in xenograft assays. Mechanistically, MACROD2 increases p300 binding to estrogen response elements in a subset of ER regulated genes. Primary breast cancers and matched metastases demonstrate MACROD2 expression can change with disease evolution, and increased expression and amplification of MACROD2 in primary tumors is associated with worse overall survival. These studies establish MACROD2 as a key mediator of estrogen independent growth and tamoxifen resistance, as well as a potential novel target for diagnostics and therapy.breast cancer | tamoxifen | resistance | MACROD2 | ER positive T he selective estrogen receptor modulator (SERM) tamoxifen is a highly effective drug for the prevention and treatment of estrogen receptor-alpha (ER) positive breast cancers (1). However, resistance to this drug remains a clinically important problem. The molecular mediators of tamoxifen resistance have not been fully elucidated. In part, this is due to the heterogeneous nature of breast cancers, resulting in multiple mechanisms of resistance. For example, past studies have demonstrated that tamoxifen resistance is mediated by differential expression of nuclear hormone receptor coregulators (2, 3), growth factor signaling crosstalk (4-7), regulation of microRNAs (8), cyclin dependent kinases (CKDs) (9), CDK inhibitors (10, 11), and more recently, acquired somatic mutations and alterations in ER (12-17). Further insight into the molecular mediators of tamoxifen and hormone therapy resistance would have great impact on the ability to target genes and pathways that could overcome drug resistance and lead to improved clinical outcomes.In this study we describe a previously unidentified gene, MACROD2, which is amplified and overexpressed in a subset of breast cancers. MACROD2 belongs to a family of genes containing a macro domain, an evolutionarily conserved protein motif (18), whose functional role until recently has been unclear. Studies have demonstrated that MACROD2 deacetylates O-acetyl-ADP ribose, a signaling molecule generated by the deacetylation of acetylated lysine residues in histones and other proteins (19). More recent work demonstrates that MACRO domain containing proteins are involved with mono-ADP ribosylation, and can regulate cell signaling pathways and modify proteins involved with gene transcription (20). Interestingly, MACROD1 (LRP16) has been implicated in modulating ER and androgen receptor (AR) signaling in prio...

“…While such systems in which mutated oncogenes are ectopically expressed under exogenous promoters have been instrumental in dissecting their oncogenic properties, they have also led to controversial results. For example, studies focused on oncogene-mediated transformation and senescence have generated conflicting data depending on whether the cancer alleles were ectopically expressed or permanently introduced in the genome of mouse or human cells (2)(3)(4)(5). To address the limitation of current models, we have used targeted homologous recombination to introduce (knock-in, KI) a panel of cancer alleles in human somatic cells.…”

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confidence: 99%

Replacement of normal with mutant alleles in the genome of normal human cells unveils mutation-specific drug responses

Nicolantonio

Arena

Gallicchio

et al. 2008

124

Mutations in oncogenes and tumor suppressor genes are responsible for tumorigenesis and represent favored therapeutic targets in oncology. We exploited homologous recombination to knock-in individual cancer mutations in the genome of nontransformed human cells. Sequential introduction of multiple mutations was also achieved, demonstrating the potential of this strategy to construct tumor progression models. Knock-in cells displayed allele-specific activation of signaling pathways and mutation-specific phenotypes different from those obtainable by ectopic oncogene expression. Profiling of a library of pharmacological agents on the mutated cells showed striking sensitivity or resistance phenotypes to pathway-targeted drugs, often matching those of tumor cells carrying equivalent cancer mutations. Thus, knock-in of single or multiple cancer alleles provides a pharmacogenomic platform for the rational design of targeted therapies.cancer mutation ͉ oncogene addiction ͉ pharmacogenomic ͉ targeted therapies ͉ tumor progression model T he construction of model systems that accurately recapitulate the genetic alterations present in human cancer is a prerequisite to understand the cellular properties imparted by the mutated alleles and to identify genotype and tumor-specific pharmacological responses. In this regard, mammalian cell lines have been widely used as model systems to functionally characterize cancer alleles carrying point mutations and to develop and validate anticancer drugs. These models typically involve the ectopic expression (by means of plasmid transfection or viral infection) of mutated cDNAs in human or mouse cells (1). Although these approaches have yielded remarkable results, they are typically hampered by at least two caveats. First, the expression is achieved by transient or stable transfection of cDNAs, often resulting in over-expression of the target allele at levels that do not recapitulate what occurs in human cancers. Second, the expression of the mutated cDNA is achieved under the control of nonendogenous viral promoters. As a result, the mutated alleles cannot be appropriately (endogenously) modulated in the target cells. While such systems in which mutated oncogenes are ectopically expressed under exogenous promoters have been instrumental in dissecting their oncogenic properties, they have also led to controversial results. For example, studies focused on oncogene-mediated transformation and senescence have generated conflicting data depending on whether the cancer alleles were ectopically expressed or permanently introduced in the genome of mouse or human cells (2-5). To address the limitation of current models, we have used targeted homologous recombination to introduce (knock-in, KI) a panel of cancer alleles in human somatic cells. Specifically, we focused on EGFR, KRAS, BRAF, and PIK3CA mutated alleles that are found in multiple cancer types. Mutant cells have then been used to study the biochemical and transforming potential of common cancer alleles and to identify genotype-specific ...