Multistep Process of Squamous Differentiation in Tracheobronchial Epithelial Cells In Vitro: Analogy with Epidermal Differentiation

Abstract

The lung, in particular the bronchial epithelium, is a major site for tumor formation in humans. Environmental factors, such as cigarette smoke, in conjunction with genetic factors are important determinants in this disease. Malignant cells exhibit alterations in their control of proliferation and differentiation. It is believed that the acquisition of defects in the regulation of these processes is important in the process of carcinogenesis. A clear insight into the basic mechanisms of the regulation of proliferation and differentiation is required to understand the molecular mechanisms involved in tumor development and in other pathological conditions. Studies using in vitro cell culture systems of tracheobronchial epithelial cells provide useful models in which to study the regulation of differentiation and proliferation. The clonogenic cells derived from the treacheobronchial epithelium are pluripotent: They have self-renewal capacity and can differentiate along either a normal, mucosecretory, or a squamous cell pathway. Squamous differentiation in tracheobronchial epithelial cells has many morphological, biochemical, and regulatory properties in common with epidermal differentiation. This pathway of differentiation is a multistep process consisting of at least three stages. In the initial stage, cells become committed to terminal cell division. This is followed by the expression of the squamous differentiated phenotype and finally cornification. Various factors, such as several growth factors, retinoids, calcium ions, and phorbol esters, regulate the program of differentiation at different stages. Studies have indicated that the controls of proliferation and differentiation are interrelated. Cell lines established from tracheobronchial epithelial cells expressing SV40 large T-antigen, as well as carcinoma cell lines, exhibit altered responses to growth and differentiation regulatory factors Alterations in the commitment to terminal cell division must be a crucial step in the transition of a normal to a malignant cell.

Response of head and neck epithelial cells to a DNA damage‐differentiation checkpoint involving polyploidization

“…Some of the cells that we have analyzed were isolated from nonsquamous epithelium (trachea). However, the capacity of human respiratory cells to undergo squamous differentiation in vivo is well known, in response to toxic or mechanic injury or deregulated proliferation . Interestingly, all primary cells, including the trachea, underwent squamous differentiation in culture in the presence of serum and growth factors that hyperactivated the cell cycle.…”

“…However, the capacity of human respiratory cells to undergo squamous differentiation in vivo is well known, in response to toxic or mechanic injury or deregulated proliferation. 3,37 Interestingly, all primary cells, including the trachea, underwent squamous differentiation in culture in the presence of serum and growth factors that hyperactivated the cell cycle. Skin grafts are used in oncologic surgery for tissue reconstruction in the trachea or esophagus, 5-8 thus indicating the mutual plasticity of these epithelia.…”

Changes in responsiveness of rat tracheal epithelial cells to transforming growth factor‐β1 with time in culture

“…However, these experiments also showed that, of the pre-plateau phase cultures, those with the highest cell density were the least TGFpl responsive. Our interpretation is that the decrease in TGFpl responsiveness may be related to the commitment of increasing numbers of cells to terminal differentiation, which begins to occur spontaneously as tracheal cell cultures enter the second half of the exponential growth phase Jetten, 1989). We recently demonstrated that this process occurs at a n accelerated rate in cultures seeded with a higher density of clonogenic cells (Gray et al, 1991).…”

A three-dimensional model of differentiation of immortalized human bronchial epithelial cells

“…Multilayering has been shown in other studies using normal bronchial epithelium (Paquette et al, 2003) and could be attributed to the culture media that are formulated to promote proliferation and inhibit differentiation. Some have suggested that retinoic acid may inhibit the skin‐like morphology of bronchial epithelium (Jetten, 1989; Sachs et al, 2003) and might be necessary for ciliary and mucous cell development (Gray et al, 1996; Koo et al, 1999). While we were successful in obtaining ciliogenesis using the current medium formulation, future modifications of the medium such as switching to a more basal media at late time points, or performing xenograft studies may result in different outcomes.…”