The Biologic Characteristics Of Neurogenesis In Breast Cancer And Its Underlying Molecular Mechanisms

OBJECTIVE We investigated the types,distribution and sources of the sprouted innervation into the breast cancer to explore the biological characteristics of neuronegesis in a rat model of breast cancer.Additionally,we investigated the involvement of nerve growth factor(NGF)and vascular endothelial growth factor(VEGF)in the neurogenesis in breast cancer via extracellular signal-regulated kinase(ERK)to explore the molecular mechanisms underlying the neurogenesis in breast cancer.METHOD Breast cancer was induced by intraperitoneal administration of MNU(50 mg/kg,once per month for twice)in 7-week-old female Sprague-Dawley rats and was determined by hematoxylin-eosin(HE)staining.The different neuronal markers including protein gene product(PGP9.5),calcitonin gene related peptide(CGRP)and vesicular monoamine transporter(VMAT2)was utilized to identify the different types of innervation into the breast cancer tissues using immunohistochemistry,immunofluorescence and western blot.The source of innervation was examined by retrograde labeling with the fluorescent dye Di I.The effects of blockage of NGF/VEGF receptors on the expression of PGP9.5 and ERK in breast cancer tissues was examined.RESULTS The 1-3 lumps appeared in either abdomen or chest 1-2 months after the first administration of MNU,confirmed as Breast cancer by HE staining.PGP9.5-,Immunohistochemistry and immunofluorescence staining showed that CGRP-and VMAT2-immunoreactive nerve fibers were mainly distributed in the tumor stroma.Western blot analysis showed that PGP9.5 protein level was increased with the growth of tumors.The nerve fibers and neurons labeled Di I were found in tumor tissues and related DRG,respectively under the fluorescence microscopy.Western blot analysis showed that administrations of VEGF receptor inhibitor(SU5416),anti-VEGFR2 antibody(a-VEGFR2)and NGF receptor inhibitor(AG879)decreased the expression of PGP 9.5 in tumor(SU5416: P<0.001;AG879: P<0.01;a-VEGFR2: P<0.001),while all of them increased the expression of ERK(SU5416: P<0.05;AG879: P<0.01;a-VEGFR2: P<0.001).CONCLUSIONS Neurogenesis did occur in tumor tissue in a rat model breast cancer.The nerve fibers including sensory afferent nerves that response to the noxious stimuli and sympathetic efferent nerves were mainly distributed in the tumor stroma.NGF and VEGF contributed to the neurogenesis in breast cancer,which is associated with the cellular signaling ERK.