Basement Membrane Integrity

In Oral Cancer

Presented by

Dr. Thein Tun

The basement membrane (BM) is a major functional

component of the extracellular matrix that underlies all

epithelia.

provides structural support to epithelia and forms a

mechanical connection between epithelia and underlying

connective tissue.

The integrity of the basement membrane is essential for

cellular growth, and is often altered in disease.

In general, basement membranes appear very similar

to each other by extracellular matrix (EM).

But all are not alike!

There is a wealth of molecular and functional

heterogeneity among basement membranes, due

primarily to isoform variations of basement

membrane components.

Remodeling of the BM is a normal process that occurs

throughout development.

The BM is structurally remodeled by cells during

movement and proliferation.

Breach of the BM is a critical step for malignant cells to

invade locally and metastasize.

• The role of the BM in carcinoma biology is not well

understood.

• Based mostly on morphologic data, the loss of BM

continuity has been associated with increasing

malignancy. (Bosman, 1994)

Four layers of the basement

membrane zone

(1) The basal keratinocyte layer,

(2) the lamina lucida,

(3) the lamina densa, and

(4) the sublamina densa (lamina reticularis).

Figure (1) basement membrane zone

Within the basal keratinocyte,

• keratin intermediate filaments (IF),

• hemidesmosomes (HD),

• composed of bullous pemphigoid antigen 1 (BPAG1),

• plectin,

• Within the lamina lucida (LL),

• anchoring filaments (AF), composed predominantly

of Laminin 332.

• the extracellular portions of collagen XVII

• Integrin and CD151.

• Within the lamina densa (LD) are

• collagen IV,

• nidogen and perlecan.

• Within the sublamina densa (lamina reticularis)

• anchoring fibrils (AFib), composed of collagen VII.

Figure (2) Basement membrane

• Lamina lucida and lamina densa together make up

basal lamina

• Within the lamina lucida, we can see thin strand-like

structures known as anchoring filaments.

• Beneath the lamina lucida is known as lamina densa.

• Beneath the lamina lucida and lamina densa is the

sublamina densa (lamina reticularis).

• The basal keratinocyte is anchored to the basal lamina

via the intermediate filaments and hemidesmosomes.

• Two types of hemidemsmosome have been identified:

• mature type I and

• immature or developing type II hemidesmosomes

• The main components of basal lamina are:

• Type IV collagen, Glycoproteins, Proteoglycans

• The Lamina Lucida is made up of laminin, integrins,

entactins, and dystroglycans.

• The Lamina Densa is made up of type IV collagen

fibers; perlecan (a heparan sulfate proteoglycan)

• Glycoproteins are variously located in the lamina lucida

and lamina densa areas. (Lee, 1988)

• Collagen VII is predominantly localized to the epidermal

basement membrane zone within the lamina densa and

sublamina densa.

• It provides structural support and stability to the

epidermal basement zone.

Many of the components of the epidermal basement

membrane zone have been linked to cancer, with

several basement membrane zone components having

a significant role in tumor invasiveness and or

prognosis. (Ko & Marinkovich, 2010)

Although cancers come in a variety of different forms,

one of the basic tenants of cancer is the fact that it has

the ability to invade through basement membranes.

• Early stages of malignancy that are thus limited to the

epithelial layer by the basement membrane are called

carcinoma in situ.

Three-Step Theory of Invasion

1. The first step is tumor cell attachment via cell surface receptors

which specifically bind to components of the matrix such as

laminin (for the basement membrane) and fibronectin (for the

stroma).(Kramer et al., 1980)

2. The anchored tumor cell next secretes hydrolytic enzymes (or

induces host cells to secrete enzymes) which can locally

degrade the matrix (including degradation of the attachment

components).

• Matrix lysis most probably takes place in a highly localized

region close to the tumor cell surface.

3. The third step is tumor cell locomotion into the region of the

matrix modified by proteolysis.

• Continued invasion of the matrix may take place by cyclic

repetition of these three steps.

• Liotta and Stetler-Stevenson have described the

following 3-step theory for the invasion of carcinoma

cells through the BM:

• (i) the tumour cells bind to the BM and extracellular

matrix;

• (ii) proteolytic enzymes degrade the BM; and

• (iii) the carcinoma cells are able to migrate and spread.

Figure-3. Step1 is tumor cell attachment to the matrix. This process may be

mediated by specific attachment factors such as laminin, which form a bridge

between the cell surface laminin receptor and type IV collagen.

Figure-4. Step 2 is local degradation of the matrix by tumor cell-associated proteases.

Such proteases may degrade both the attachment proteins as well as the structural

collagenous proteins of the matrix. Proteolysis may be localized at the tumor cell

surface where the amount of active enzyme outbalances the natural protease

inhibitors present in the matrix.

Figure-5. Step 3 is tumor cell locomotion into the region of the matrix

modified by proteolysis. The direction of locomotion may be influenced by

chemotatic factors. Continued invasion of the extracellular matrix may take

place by cyclic repetition of these three steps.

• The laminins are important integrin-binding structures

within the lamina lucida and lamina densa.

• Laminins are large glycoproteins composed of three

chains (α,β and ϒ ) bound by disulfide bonds.

• There are at least 15 different laminins, comprised of a

combination of 5 different α-chains, three β-chains, and

three γ-chains.

• laminin-332, when up regulated may serve as a

promoter of tumor invasiveness, and when down

regulated, the basement membrane zone's integrity is

altered such that tumor cells are allowed to cross the

basement membrane.

• laminin-5 (Ln-5) plays a vital role in tumour

migration and shows an increased expression in areas

of direct tumour–stroma interactions in OSCCs.

(Berndt et al., 2001)

• Laminins are important autocrine factors produced by

cancers to promote tumorigenesis.

• Invasion of OSCCs is associated with Ln-5 synthesis,

focal loss from the basement membrane, and

deposition in the stroma beneath invading carcinoma

cell complexes. (Franz et al., 2007)

• Laminin-5 is a component of the epithelial cell adhesion

complex containing hemidesmosomes, anchoring fibrils

and anchoring fibers. (Gerecke et al., 1994)

• Laminin-5 connects the hemidesmosomes with the

underlying connective tissue through type VII collagen

(Fig. 7). (Rousselle et al., 1997)

Figure (7) describes the adhesion of integrin (Int) to the laminin-5 (Ln-5).

• Integrin is located to the cell membrane and adhered to the laminin-5,

which, in turn, is adhered to the type VII collagen (VII).

• Type VII collagen forms the lamina fibroreticularis-layer outside the

BM lamina densa.

• Integrin is a two-way signaling molecule that links

the keratinocyte cytoskeleton to the extracellular

matrix.

• Integrin expression by cancer cells at the invasive

front has been related to the mode of invasion and

prognosis in OSCC.

• OSCC patients with higher expression levels of α3,

α6 and β1 integrins have significantly better

prognosis than those with lower expression levels.

• In addition, β1 integrin expression showed the highest

correlation with clinical and pathological

characteristics.(Ohara et al., 2009)

• They are necessary for maintaining epidermal

homeostatic functions such as adhesion, proliferation, and

differentiation.

• Integrin-laminin interactions maintain stem cell

populations and help to ensure their stability.

• Epithelial cells interact with the basement membrane via

integrins along their basal surface.

• Other molecules found within the lamina densa layer

of the basement membrane zone include nidogens

and perlecan.

• These molecules play a supportive role in the

stabilization of the basement membrane.(Kruegel and

Miosge, 2010)

• Nidogens play a supportive role.

• Their primary function appears to be stabilizing

interactions between laminins and collagen IV with the

lamina densa.

• Nidogens are not required for epidermal basement

membrane zone formation.

• Perlecan has also been implicated in tumorigenesis.

• Perlecan expression is increased in liver tumors, oral

tumors, and serves as a promoter of tumor growth and

angiogenesis. (Iozzo et al., 2009)

• Perlecan can serve as both an enhancer of, or an inhibitor

of angiogenesis.

• Angiogenesis is promoted by the binding of perlecan to

growth factor receptors.(Theocharis et al., 2010)

• Other basement membrane zone molecules such as

CD151, nidogen, and perlecan are associated with

tumorigenesis.

Conclusion

• During the development of invasive cancer, tumour

cells have to penetrate the extracellular matrix including

the basement membrane (BM).

• Tumour cells are hypothesized to traverse basement

membranes by a three-step process: attachment, local

degradation of the basement membrane by type IV

collagenase and other proteases, and locomotion.

• In consequence, the invasion of carcinoma cells

through the BM must be either an active process

effected by the carcinoma cells themselves or is

mediated by structural alterations of the BM occurring

during carcinogenesis and cancer progression.

• It was supposed that invading carcinoma cells are able

to degrade actively the continuous BM by secreting

collagenase and other proteolytic enzymes.

References

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Thank you