Hypothetical involvement of stress hormones-induced reprograming of adult stem/progenitor cells in tumorigenesis

Stress is a state of threatened or perceived as threatened homeostasis that can be induced by various external and internal stimuli such as psychosocial factors, inflammatory or injurious conditions, and infections. In order to restore body homeostasis, adrenal glands produce and secrete glucocorticoids (GCs) and catecholamines (CAs), which are the main stress hormones that support the survival and adaptation of the organisms to the new environment. In contrast to the rather beneficial impact of acute and short-lasting stress, chronic stress and related dysregulation of the stress system is implicated in the development of many non-communicable diseases, including cancer. Particularly, ever-increasing experimental and clinical evidence implicates the involvement of CAs and GCs as well as the overexpression of their receptors in the activation of the major pathways involved in tumour development, metastasis, and resistance to various therapies. More importantly, results of experimental and epidemiological studies revealed that overexposure to stress hormones during pre- and early postnatal life might induce life-long or even transgenerational dysregulation of the stress system and predispose it to the development of various tumours. Although the exact mechanisms involved in the latter process are not yet fully known, it has been demonstrated that GC-induced epigenetic modifications can change the expression of several key genes involved in the regulation of the stress system, tumour initiation, and epigenetic imprinting. When such alterations occur in stem/progenitor cells (SPCs), this might not only lead to long-term dysfunction of the stress system but might promote the generation of cancer stem cells (CSCs). This review article discusses a hypothesis that stress hormones-mediated epigenetic reprograming of various SPCs during sensitive developmental periods, might contribute to their dysfunction and increased sensitivity to malignant transformation, thereby promoting tumorigenesis.