Integrins are heterodimeric extracellular matrix receptors that are essential for the proper development of the vertebrate nervous system. We report here that selective loss of integrin β1 in excitatory neurons leads to reductions in the size and complexity of hippocampal dendritic arbors, hippocampal synapse loss, impaired hippocampus-dependent learning, and exaggerated psychomotor sensitivity to cocaine in mice. Our biochemical and genetic experiments demonstrate that the intracellular tail of integrin β1 binds directly to Arg kinase, and that this interaction stimulates activity of the Arg substrate p190RhoGAP, an inactivator of the RhoA GTPase. Moreover, genetic manipulations that reduce integrin β1 signaling through Arg recapitulate the integrin β1 knockout phenotype in a gene-dose sensitive manner. Together, these results describe a novel integrin β1-Arg-p190RhoGAP pathway that regulates dendritic arbor size, promotes synapse maintenance, supports proper hippocampal function, and mitigates the behavioral consequences of cocaine exposure.

Adolescence is characterized by vulnerability to the development of neuropsychiatric disorders including drug addiction, as well as prefrontal cortical refinement that culminates in structural stability in adulthood. Neuronal refinement and stabilization are hypothesized to confer resilience to poor decision making and addictive-like behaviors, although intracellular mechanisms are largely unknown. We characterized layer V prefrontal dendritic spine development and refinement in adolescent wild-type mice and mice lacking the cytoskeletal regulatory protein Abl-related gene (Arg) kinase. Relative to hippocampal CA1 pyramidal neurons, which exhibited a nearly linear increase in spine density up to postnatal day 60 (P60), wild-type prefrontal spine density peaked at P31, and then declined by 18% by P56 –P60. In contrast, dendritic spines in mice lacking Arg destabilized by P31, leading to a net loss in both structures. Destabilization corresponded temporally to the emergence of exaggerated psychomotor sensitivity to cocaine. Moreover, cocaine reduced dendritic spine density in wild-type orbitofrontal cortex and enlarged remaining spine heads, but arg −/− spines were unresponsive. Local application of Arg or actin polymerization inhibitors exaggerated cocaine sensitization, as did reduced gene dosage of the Arg substrate, p190RhoGAP. Genetic and pharmacological Arg inhibition also retarded instrumental reversal learning and potentiated responding for reward-related cues, providing evidence that Arg regulates both psychomotor sensitization and decision-making processes implicated in addiction. These findings also indicate that structural refinement in the adolescent orbitofrontal cortex mitigates psychostimulant sensitivity and support the emerging perspective that the structural response to cocaine may, at any age, have behaviorally protective consequences.

Tumor progression is a complex, multistep process involving accumulation of genetic aberrations and alterations in gene-expression patterns leading to uncontrolled cell division, invasion into surrounding tissue and finally dissemination and metastasis. We have previously shown that the Arg/Abl2 non-receptor tyrosine kinase acts downstream of the EGF receptor and Src tyrosine kinases to promote invadopodium function in breast cancer cells, thereby promoting their invasiveness. However, whether and how Arg contributes to tumor development and dissemination in vivo has never been investigated. Using a mouse xenograft model, we show that knocking down Arg in breast cancer cells leads to increased tumor cell proliferation and significantly enlarged tumor size. Despite having larger tumors, the Arg knockdown tumor-bearing mice exhibit significant reductions in tumor cell invasion, intravasation into blood vessels, and spontaneous metastasis to lungs. Interestingly, we found that proliferation-associated genes in the Ras-MAPK pathway are upregulated in Arg-knockdown breast cancer cells, as is Ras-MAPK signaling, while invasion-associated genes are significantly downregulated. These data suggest that Arg promotes tumor cell invasion and dissemination, while simultaneously inhibiting tumor growth. We propose that Arg acts as a switch in metastatic cancer cells that governs the decision to “grow or go” (divide or invade).

Fibroblast activation protein (FAP) is a cell-surface serine protease highly expressed on cancer-associated fibroblasts of human epithelial carcinomas but not on normal fibroblasts, normal tissues, and cancer cells. We report herein a novel FAP-triggered photodynamic molecular beacon (FAP-PPB) comprising of a fluorescent photosensitizer and a black hole quencher 3 linked by a peptide sequence (TSGPNQEQK) specific to FAP. FAP-PPB was effectively cleaved by both human FAP and murine FAP. Using the HEK293 transfected cells (HEK-mFAP, FAP+; HEK-Vector, FAP−), systematic in vitro and in vivo experiments validated the FAP-specific activation of FAP-PPB in cancer cells and mouse xenografts, respectively. FAP-PPB was cleaved by FAP, allowing fluorescence restoration in FAP-expressing cells, while leaving non-expressing FAP cells undetectable. Moreover, FAP-PPB showed FAP-specific photocytotoxicity toward HEK-mFAP cells whereas it was non-cytotoxic toward HEK-Vector cells. This study suggests that the FAP-PPB is a potentially useful tool for epithelial cancer detection and treatment.