Lung Cancers: Parenchymal Biochemistry and Mechanics

Abstract

Parenchyma of pulmonary cancers acquires contractile properties that resemble those of muscles but presents some particularities. These non-muscle contractile tissues could be stimulated either electrically or chemically (KCl). They present the Frank-Starling mechanism, the Hill hyperbolic tension-velocity relationship, and the tridimensional time-independent tension-velocity-length relationship. Relaxation could be obtained by the inhibition of crossbridge molecular motors or by a decrease in the intracellular calcium concentration. They differ from muscles in that their kinetics are ultraslow as evidenced by their low shortening velocity and myosin ATPase activity. Contractility is generated by non-muscle myosin type II A and II B. The activation of the β-catenin/WNT pathway is accompanied by the high level of the non-muscle myosin observed in lung cancers.

Keywords: canonical WNT pathway; lung cancer; mechanics; myofibroblast; non-muscle myosin; β-catenin.

Figure 1

Electronic set-up, SMA-NMIIA-B cycle, and schematic SMA-NM IIA-B sliding mechanism. (A) Electronic set-up showing the experimental non-muscle system. (B) NMII-CB cycle. The CB cycle was composed of six different conformational steps, i.e., three detached steps (D1, D2, and D3) and three attached steps (A1, A2, and A3). The myosin molecular motor was non-muscle myosin type IIA (NMIIA) and IIB (NMIIB). The power stroke was characterized by the generation of a unitary CB force and the CB step. The power stroke occurred with a tilt of the NMII head and produced a force of a few pico Newtons and a displacement of a few nanometers. Importantly, the kinetics of NMII were extremely slow. (C) NMII binds with actin through the head domain of the heavy chain. Importantly, NMIIA and B molecules assembled into bipolar filaments, allowing myosin to slide along actin in an anti-parallel manner. A tilt of the motor domain enabled a conformational change that moved actin filaments in an anti-parallel manner. The ATP molecule formed a bond with the NMII-ATPase site located on the motor domain. This allowed the dissociation of actin from the NMII head. ATP was then hydrolyzed and subsequently NMII formed a bond with actin. Then, the power stroke occurred with a tilt of the NMII head, which generated a CB single force and a displacement of a few nanometers. ADP was then released from the actin–NMII complex. A new ATP molecule dissociated actin from the motor domain, and a new CB cycle began.

Figure 2

Squamous cell carcinoma of lung and peritumoral stroma. Magnification ×20, HES staining. The tumor proliferation (blue arrow) was composed of dense masses of cohesive squamous cells of tumor origin. It was surrounded by a peritumoral reactive stroma (black arrow) consisting of a fibrous background and a dense lympho-plasmacytic infiltrate.

Figure 3

Expression of SMA, β-catenin, NM-IIB, and NM-IIA. Magnification ×20. (A) Staining of the tumor stroma by SMA (black arrow). There was no significant staining of tumor cells (blue arrow). Smooth muscle actin (SMA) marked the myofibroblasts. (B) β-catenin: tumor cells exhibited intense membranous staining of β-catenin (blue arrow). The stroma showed a weak staining (black arrow), compared with that of tumor cells. (C) NM-IIB: Membranous staining was observed in tumor cells (blue arrow) and peritumoral stroma (black arrow). (D) NM-IIA: Membranous staining was observed in tumor cells (blue arrow) and peritumoral stroma (black arrow).

Figure 4

Parameters of contraction under tetanic stimulation: shortening length (blue curve) rapidly reached a maximum. Then, an isometric load clamp was imposed. The shortening length returned rapidly to the resting length and the tension curve (green) developed the maximum isometric tension.

Figure 5

The Frank–Starling mechanism and the Hill hyperbolic relationship. (Left): The Frank–Starling curve represents the isometric tension as a function of initial length. Triangle: control values; circle: after inotropic effect (1 mM KCl). After the inotropic effect, the Frank–Starling curve was above the control curve and with a steeper slope. (Right): the Hill relationship. The tension–velocity (T–V) relationship describes a hyperbola.

Figure 6

The tridimensional length–velocity–tension relationship. Length (A) and tension (B) are represented as a function of time; in addition, the phase-plane velocity–length (V–L) (C) was also drawn. Two curves were imposed with different loading conditions: curve 1 with a constant load (preload), and curve 2 with an afterload higher than the preload of curve 1 and clamped to the preload, i.e., at the same load level as that of curve 1. After a brief overshoot, the trajectories of curves 1 and 2 were superposed on the V–L phase-plane diagram (blue curve), but occurred at two different times on the length curve according to time (t1 and t2). On the V–L phase-plane (C) and after an overshoot, curve 2 followed the same trace as curve 1, before it dissociated from curve 1.

Figure 7

Relaxation of lung samples. L: Length; F: Force. (A) Isotonic relaxation obtained with ISDN; (B) isotonic relaxation obtained with BDM; (C) isometric relaxation obtained with BDM.